bluuebunny/crossref_metadata_2025 huggingface dataset:
The origins of acquired immune deficiency syndrome viruses: where and when?
Authors: Sharp Paul M. , Bailes Elizabeth , Chaudhuri Roy R. , Rodenburg Cynthia M. , Santiago Mario O. , Hahn Beatrice H.
Published: September 2002

In the absence of direct epidemiological evidence, molecular evolutionary studies of primate lentiviruses provide the most definitive information about the origins of human immunodeficiency virus (HIV)–1 and HIV–2. Related lentiviruses have been found infecting numerous species of primates in sub–Saharan Africa. The only species naturally infected with viruses closely related to HIV–2 is the sooty mangabey (Cercocebus atys) from western Africa, the region where HIV–2 is known to be endemic. Similarly, the only viruses very closely related to HIV–1 have been isolated from chimpanzees (Pan troglodytes), and in particular those from western equatorial Africa, again coinciding with the region that appears to be the hearth of the HIV–1 pandemic. HIV–1 and HIV–2 have each arisen several times: in the case of HIV–1, the three groups (M, N and O) are the result of independent cross–species transmission events. Consistent with the phylogenetic position of a ‘fossil’ virus from 1959, molecular clock analyses using realistic models of HIV–1 sequence evolution place the last common ancestor of the M group prior to 1940, and several lines of evidence indicate that the jump from chimpanzees to humans occurred before then. Both the inferred geographical origin of HIV–1 and the timing of the cross–species transmission are inconsistent with the suggestion that oral polio vaccines, putatively contaminated with viruses from chimpanzees in eastern equatorial Africa in the late 1950s, could be responsible for the origin of acquired immune deficiency syndrome.
The origin of acquired immune deficiency syndrome: Darwinian or Lamarckian?
Authors: Burr Tom , Hyman J. M. , Myers Gerald
Published: September 2002

The subtypes of human immunodeficiency virus type 1 (HIV–1) group M exhibit a remarkable similarity in their between–subtype distances, which we refer to as high synchrony. The shape of the phylogenetic tree of these subtypes is referred to as a sunburst to distinguish it from a simple star phylogeny. Neither a sunburst pattern nor a comparable degree of symmetry is seen in a natural process such as in feline immunodeficiency virus evolution. We therefore have undertaken forward–process simulation studies employing coalescent theory to investigate whether such highly synchronized subtypes could be readily produced by natural Darwinian evolution. The forward model includes both classical (macro) and molecular (micro) epidemiological components. HIV–1 group M subtype synchrony is quantified using the standard deviation of the between–subtype distances and the average of the within–subtype distances. Highly synchronized subtypes and a sunburst phylogeny are not observed in our simulated data, leading to the conclusion that a quasi–Lamarckian, punctuated event occurred. The natural transfer theory for the origin of human acquired immune deficiency syndrome (AIDS) cannot easily be reconciled with these findings and it is as if a recent non–Darwinian process took place coincident with the rise of AIDS in Africa.
Gene flow in wild chimpanzee populations: what genetic data tell us about chimpanzee movement over space and time
Authors: Gagneux Pascal , Gonder M. Katherine , Goldberg Tony L. , Morin Phillip A.
Published: September 2002

The isolation of phylogenetically distinct primate immunodeficiency viruses from at least seven wild–born, captive chimpanzees indicates that viruses closely related to HIV–1 may be endemic in some wild chimpanzee populations. The search for the chimpanzee population or populations harbouring these viruses is therefore on. This paper attempts to answer the question of whether or not such populations of chimpanzees are likely to exist at all, and, if so, where they are likely to be found. We summarize what is known about gene flow in wild populations of chimpanzees, both between major phylogeographical subdivisions of the species, and within these subdivisions. Our analysis indicates that hitherto undocumented reproductively isolated chimpanzee populations may in fact exist. This conclusion is based on the observation that, despite limited geographical sampling and limited numbers of genetic loci, conventional notions of the nature and extent of chimpanzee gene flow have recently been substantially revised. Molecular genetic studies using mitochondrial DNA sequences and hypervariable nuclear microsatellite markers have indicated the existence of heretofore undocumented barriers to chimpanzee gene flow. These studies have identified at least one population of chimpanzees genetically distinct enough to be classified into a new subspecies (Pan troglodytes vellerosus). At the same time, they have called into question the long–accepted genetic distinction between eastern chimpanzees (Pan troglodytes schweinfurthii) and western equatorial chimpanzees (Pan troglodytes troglodytes). The same studies have further indicated that gene flow between local populations is more extensive than was previously thought, and follows patterns sometimes inconsistent with those documented through direct behavioural observation. Given the apparently incomplete nature of the current understanding of chimpanzee gene flow in equatorial Africa, it seems reasonable to speculate that a chimpanzee population or populations may exist which both harbour the putative HIV–1 ancestor, and which have remained reproductively isolated from other chimpanzee populations over the time–scale relevant to the evolution of the SIVcpz–HIV–1 complex of viruses. Continued extensive sampling of wild chimpanzee populations, both for their genes and their viruses, should be performed quickly considering the high probability of extinction that many wild chimpanzee populations face today. The history of human–chimpanzee contacts is discussed.
Infectious disease dynamics: what characterizes a successful invader?
Authors: May Robert M. , Gupta Sunetra , McLean Angela R.
Published: September 2002

Against the background of human immunodeficiency virus (HIV) and acquired immune deficiency syndrome (AIDS) and other potentially emerging (or re–emerging) infectious diseases, this review will focus on the properties which enable an infectious agent to establish and maintain itself within a specified host population. We shall emphasize that for a pathogen to cross a species barrier is one thing, but for it successfully to maintain itself in the new population is must have a ‘basic reproductive number’,R0, which satisfiesR0> 1. We shall further discuss how behavioural factors interweave with the basic biology of the production of transmission stages by the pathogen, all subject to possible secular changes, to determine the magnitude ofR0. Although primarily focusing on HIV and AIDS, we shall review wider aspects of these questions.
Serial human passage of simian immunodeficiency virus by unsterile injections and the emergence of epidemic human immunodeficiency virus in Africa
Authors: Marx Preston A. , Alcabes Phillip G. , Drucker Ernest
Published: September 2002

There is compelling evidence that both human immunodeficiency virus (HIV) types emerged from two dissimilar simian immunodeficiency viruses (SIVs) in separate geographical regions of Africa. Each of the two HIVs has its own simian progenitor and specific genetic precursor, and all of the primates that carry these SIVs have been in close contact with humans for thousands of years without the emergence of epidemic HIV. To date no plausible mechanism has been identified to account for the sudden emergence in the mid–20th century of these epidemic HIVs. In this study we examine the conditions needed for SIV to complete the genetic transition from individual human SIV infections to epidemic HIV in humans. The genetic distance from SIV to HIV and the mutational activity needed to achieve this degree of adaptation to human hosts is placed within a mathematical model to estimate the probabilities of SIV completing this transition within a single SIV–infected human host. We found that the emergence of even one epidemic HIV strain, following a single human exposure to SIV, was very unlikely. And the probability of four or more such transitions (i.e. HIV–1 groups M, O and HIV–2 subtypes A and B) occurring in a brief period is vanishingly small. We conclude that SIV cannot become a zoonosis, but requires adaptive mutations to become HIV. Some modern event must have aided in the transition of SIV to HIV. Our research indicates that serial passage of partially adapted SIV between humans could produce the series of cumulative mutations sufficient for the emergence of epidemic HIV strains. We examined the rapid growth of unsterile injections in Africa beginning in the 1950s as a biologically plausible event capable of greatly increasing serial human passage of SIV and generating HIV by a series of multiple genetic transitions. We conclude that increased unsterile injecting in Africa during the period 1950–1970 provided the agent for SIV human infections to emerge as epidemic HIV in the modern era.
The burden of proof and the origin of acquired immune deficiency syndrome
Authors: Martin Brian
Published: September 2002

There is a distinct difference in the way that different theories about the origin of acquired immune deficiency syndrome have been treated, with the widely supported cut–hunter theory given relatively little scrutiny, while the oral polio vaccine theory has been subject to intense criticism. This difference in treatment cannot be explained as application of the scientific method. A better explanation is that the burden of proof is put on all contenders to the cut–hunter theory, giving it an unfair advantage, especially given that this assignment of the burden of proof appears to reflect non–scientific factors.
Hypotheses and facts
Authors: Koprowski Hilary
Published: September 2002

The book,
The river
, is based on assumptions and not facts. Oral polio vaccine was produced entirely in rhesus monkey kidney cell cultures. Allegations that it was produced in chimpanzee kidneys at the Wistar Institute in Philadelphia or, alternatively, that the vaccine was made in the then Belgian Congo in chimpanzee kidney has no basis in fact. As the only witness to the historical events leading to the development of oral polio vaccine, I have demonstrated in this paper the truthful facts excluding any link between oral polio vaccine and human immunodeficiency virus.
Natural and iatrogenic factors in human immunodeficiency virus transmission
Authors: Weiss Robin A.
Published: September 2002

In the light of the evidence and discussion presented during The Royal Society Discussion Meeting it seems to me that the oral polio vaccine (OPV) hypothesis for the origins of human immunodeficiency virus (HIV) and the acquired immune deficiency syndrome epidemic is less tenable now than one year earlier. The OPV hypothesis does not accord with HIV phylogenetic studies: the geographical correlation has been challenged; the testimony of those directly involved with OPV trial vaccines denies the use of chimpanzees, corroborating tests on the still–available vials of the CHAT vaccines, which contain neither simian immunodeficiency virus nor chimpanzee DNA. Yet one lesson to be learned from considering OPV as a source of HIV is how plausibly it might have happened and how cautious we need to be over introducing medical treatments derived from animal tissues, such as live, attenuated vaccines or xenotransplantation. To cast doubt on the OPV hypothesis is not to dismiss entirely the role of iatrogenic factors in HIV transmission from chimpanzees in the first instance, in HIV adaptation to onward transmission during its early phase in humans, or in the later spread of HIV to patients, for example, with haemophilia. To reduce the argument over the origins of HIV to the ‘OPV hypothesis’ versus the ‘cut–hunter hypothesis’ is an oversimplistic and false antithesis. Both natural and iatrogenic transmission of many retroviruses, including HIV, have been thoroughly documented and are not mutually exclusive. Exactly how, when and where the first human(s) became infected with the progenitor of HIV–1 group M, which gave rise to the pandemic strain, is likely, however, to remain a matter of conjecture.
Simian immunodeficiency virus in kidney cell cultures from highly infected rhesus macaques (
Macaca mulatta
)
Authors: Lena Philippe , Luciw Paul
Published: September 2002

Trace amounts of simian immunodeficiency virus (SIV) proviral DNA were detected in monolayers of primary kidney cells from two rhesus macaques (
Macaca mulatta
) heavily infected with the highly pathogenic strain SIVmac251. There was no detectable infectious SIV in the supernatant from the kidney cell cultures obtained from either monkey. However, infectious SIV was rescued by co–culture of kidney cells with a permissive lymphoid cell line. Macrophages, present in these cultures, may be the reservoir for the proviral genomes.
Vaccine could not have been prepared in Stanleyville
Authors: Osterrieth Paul M.
Published: September 2002

In Stanleyville, at the time of vaccination campaigns, tissue cultures were primitive, experimental and used solely for diagnostic purposes. Production of vaccine was impossible to carry out. A few chimpanzee kidneys were minced and sent to Philadelphia as part of the hepatitis experiments of Dr Deinhardt. Vaccine was never handled in my laboratory and contamination with chimpanzee cells was not possible.
Responsibility for truth in research
Authors: Nelson–Rees Walter A.
Published: September 2002

For over half a century, cell cultures derived from animals and humans have served researchers in various fields. To this day, cross–contamination of cultures has plagued many researchers, often leading to mistaken results, retractions of results, cover–ups and some out–and–out falsification of data and results following inadvertent use of the wrong cells. Also, during years of examining cultures for purity we learned that many virologists were not too concerned about the specificity of the cultures they used to propagate the particular virus under study as long as the substrate (whatever it might have been) gave optimal virus yield. Polio virus propagates in primate cells, and much research has involved cells from man and various species of primates. In the 1950s a large number of chimpanzees were held in captivity in Africa for extensive studies of the efficacy of polio vaccine in production at the Wistar Institute in Philadelphia and elsewhere. Chimpanzee tissues, particularly kidneys, were thus readily available and could have also provided substrates for polio virus production, since little was known about the purity of substrates and little attention was paid to their specificity at that time.
The Jezierski papers: live polio vaccine development in colobus monkey cells but not chimpanzee cells in the Belgian Congo, 1952–1958
Authors: Desmyter Jan , Teuwen Dirk E.
Published: September 2002

A reading of ten relevant papers by Alexandre Jezierski provides evidence for the only attempt in Central Africa to develop a live oral polio vaccine (OPV) from growing reference wild polio strains to 210 passages in colobus monkey tissue culture, and experimental administration to about 25 humans. Chimpanzees were used as a human model, but their tissues or kidneys were absent from the passage and production line of the proposed vaccine. Thus, the implication published by Hooper that Jezierski had produced a candidate OPV that might have contained chimpanzee viruses, possibly simian immunodeficiency virus cpz or the precursor of human immunodeficiency virus-1 group M, is incorrect.
Postscript relating to new allegations made by Edward Hooper at The Royal Society Discussion Meeting on 11 September 2000
Authors: Plotkin Stanley A. , Teuwen Dirk E. , Prinzie Abel , Desmyter Jan
Published: September 2002

At The Royal Society Discussion Meeting,Origins of HIV and the AIDS epidemic, which this issue records, Edward Hooper added two new ‘smoking guns’ to the accusations published previously inThe river. These were proposed as conclusive evidence for the hypothesis that simian immunodeficiency virus–contaminated CHAT polio vaccine caused the HIV–1 group M epidemic. We have investigated the facts in relation to these ‘smoking guns’.
The earliest cases of human immunodeficiency virus type 1 group M in Congo-Kinshasa, Rwanda and Burundi and the origin of acquired immune deficiency syndrome
Authors: Vangroenweghe Daniel
Published: September 2002

The early cases of acquired immune deficiency syndrome and human immunodeficiency virus type 1 (HIV–1) infection in the 1960s and 1970s in Congo–Kinshasa (Zaire), Rwanda and Burundi are reviewed. These countries appear to be the source of the HIV–1 group M epidemic, which then spread outwards to neighbouring Tanzania and Uganda in the east, and Congo–Brazzaville in the west. Further spread to Haiti and onwards to the USA can be explained by the hundreds of single men from Haiti who participated in the UNESCO educational programme in the Congo between 1960 and 1975.
The distribution of early acquired immune deficiency syndrome cases and conditions for the establishment of new epidemics
Authors: Low–Beer Daniel
Published: September 2002

This article presents discussion on two issues: the distribution of early cases of acquired immune deficiency syndrome (AIDS), and the epidemiological conditions for the establishment of new diseases. Evidence from four presentations on early AIDS cases is discussed, together with issues of interpreting association and inferring causation. In the second section, the results of a stochastic epidemiological model using the ‘real’ geography of villages in northern Zaire is presented. This is used to investigate the conditions under which newly introduced infections with different characteristics are able to establish in human populations. It highlights additional spatial, temporal and behavioural conditions necessary for the persistence of introduced diseases, in addition to the condition that the basic reproductive rate
R
0
> 1.
The origin of acquired immune deficiency syndrome: can science afford to ignore it?
Authors: Cribb Julian
Published: September 2002

There is a crisis of public faith in science and scientists. Recent research shows concern over scientific ethics, transparency and who benefits from research and development, exemplified in the genetically modified organism debate. Scientific discussion of the polio vaccine hypothesis for the origin of acquired immune deficiency syndrome (AIDS) has been systematically suppressed for more than 12 years. The author calls for an international multidisciplinary inquiry into the origin of AIDS, arguing it is essential to human health, prevention of new pandemics, and to protect the integrity of science in the eyes of the public.
Concerning the early and current spread of human immunodeficiency virus type 1 and the scientific burden of proof versus the burden of current human immunodeficiency virus incidence
Authors: Bernard Roger P.
Published: September 2002

The following points were made during the Discussion that followed the paper by Brian Martin.
Man, monkeys and malaria
Authors: Gilks Charles
Published: September 2002

Bizarre though it may now seem, in the last century a whole series of experiments was conducted that involved injecting fresh monkey blood into human volunteers or patients. The reasons, valid at the time, were either to treat neurosyphilis with a relatively benign simian malaria infection (so–called pyrogen therapy), or to establish which monkey malaria species were potential zoonotic reservoirs of infection that then may have interfered with malaria eradication campaigns. Although direct inoculation of fresh blood is the most effective way of retroviruses as well as malaria parasites crossing the species barrier, this hypothesis was never taken up or researched. Unlikely, but not disproved, it is important to remember some of the more hazardous experiments that were done in good faith, too long ago to be recorded on electronic databases.
Evidence concerning how neurons of the perirhinal cortex may effect familiarity discrimination
Authors: Brown M. W. , Bashir Z. I.
Published: September 2002

Many studies indicate that recognition memory involves at least two separable processes, familiarity discrimination and recollection. Aspects of what is known of potential neuronal substrates of familiarity discrimination are reviewed. Lesion studies have established that familiarity discrimination for individual visual stimuli is effected by a system centred on the perirhinal cortex of the temporal lobe. The fundamental change that encodes prior occurrence of such stimuli appears to be a reduction in the response of neurons in anterior inferior temporal (including perirhinal) cortex when a stimulus is repeated. The neuronal responses rapidly signal the presence of a novel stimulus, and are evidence of long–lasting learning after a single exposure. Computational modelling indicates that a neuronal network based on such a change in responsiveness is potentially highly efficient in information theoretic terms. Processes that occur in long–term depression within the perirhinal cortex provide candidate synaptic plastic mechanisms for that underlying the change, but such linkage remains to be experimentally established.
The neural selection and control of saccades by the frontal eye field
Authors: Schall Jeffrey D.
Published: September 2002

Recent research has provided new insights into the neural processes that select the target for and control the production of a shift of gaze. Being a key node in the network that subserves visual processing and saccade production, the frontal eye field (FEF) has been an effective area in which to monitor these processes. Certain neurons in the FEF signal the location of conspicuous or meaningful stimuli that may be the targets for saccades. Other neurons control whether and when the gaze shifts. The existence of distinct neural processes for visual selection and saccade production is necessary to explain the flexibility of visually guided behaviour.
The prefrontal cortex: categories, concepts and cognition
Authors: Miller Earl K. , Freedman David J. , Wallis Jonathan D.
Published: September 2002

The ability to generalize behaviour–guiding principles and concepts from experience is key to intelligent, goal–directed behaviour. It allows us to deal efficiently with a complex world and to adapt readily to novel situations. We review evidence that the prefrontal cortex—the cortical area that reaches its greatest elaboration in primates—plays a central part in acquiring and representing this information. The prefrontal cortex receives highly processed information from all major forebrain systems, and neurophysiological studies suggest that it synthesizes this into representations of learned task contingencies, concepts and task rules. In short, the prefrontal cortex seems to underlie our internal representations of the ‘rules of the game’. This may provide the necessary foundation for the complex behaviour of primates, in whom this structure is most elaborate.
Exploring the cortical evidence of a sensory–discrimination process
Authors: Romo Ranulfo , Hernández Adrián , Zainos Antonio , Brody Carlos , Salinas Emilio
Published: September 2002

Humans and monkeys have similar abilities to discriminate the difference in frequency between two consecutive mechanical vibrations applied to their fingertips. This task can be conceived as a chain of neural operations: encoding the two consecutive stimuli, maintaining the first stimulus in working memory, comparing the second stimulus with the memory trace left by the first stimulus and communicating the result of the comparison to the motor apparatus. We studied this chain of neural operations by recording and manipulating neurons from different areas of the cerebral cortex while monkeys performed the task. The results indicate that neurons of the primary somatosensory cortex (S1) generate a neural representation of vibrotactile stimuli which correlates closely with psychophysical performance. Discrimination based on microstimulation patterns injected into clusters of S1 neurons is indistinguishable from that produced by natural stimuli. Neurons from the secondary somatosensory cortex (S2), prefrontal cortex and medial premotor cortex (MPC) display at different times the trace of the first stimulus during the working–memory component of the task. Neurons from S2 and MPC appear to show the comparison between the two stimuli and correlate with the behavioural decisions. These neural operations may contribute to the sensory–discrimination process studied here.
Role of uncertainty in sensorimotor control
Authors: van Beers Robert J. , Baraduc Pierre , Wolpert Daniel M.
Published: September 2002

Neural signals are corrupted by noise and this places limits on information processing. We review the processes involved in goal–directed movements and how neural noise and uncertainty determine aspects of our behaviour. First, noise in sensory signals limits perception. We show that, when localizing our hand, the central nervous system (CNS) integrates visual and proprioceptive information, each with different noise properties, in a way that minimizes the uncertainty in the overall estimate. Second, noise in motor commands leads to inaccurate movements. We review an optimal–control framework, known as ‘task optimization in the presence of signal–dependent noise’, which assumes that movements are planned so as to minimize the deleterious consequences of noise and thereby minimize inaccuracy. Third, during movement, sensory and motor signals have to be integrated to allow estimation of the body's state. Models are presented that show how these signals are optimally combined. Finally, we review how the CNS deals with noise at the neural and network levels. In all of these processes, the CNS carries out the tasks in such a way that the detrimental effects of noise are minimized. This shows that it is important to consider effects at the neural level in order to understand performance at the behavioural level.
The neural basis of episodic memory: evidence from functional neuroimaging
Authors: Rugg Michael D. , Otten Leun J. , Henson Richard N. A.
Published: September 2002

We review some of our recent research using functional neuroimaging to investigate neural activity supporting the encoding and retrieval of episodic memories, that is, memories for unique events. Findings from studies of encoding indicate that, at the cortical level, the regions responsible for the effective encoding of a stimulus event as an episodic memory include some of the regions that are also engaged to process the event ‘online’. Thus, it appears that there is no single cortical site or circuit responsible for episodic encoding. The results of retrieval studies indicate that successful recollection of episodic information is associated with activation of lateral parietal cortex, along with more variable patterns of activity in dorsolateral and anterior prefrontal cortex. Whereas parietal regions may play a part in the representation of retrieved information, prefrontal areas appear to support processes that act on the products of retrieval to align behaviour with the demands of the retrieval task.
The role of attention in visual processing
Authors: Maunsell John H. R. , Cook Erik P.
Published: September 2002

Attention to a visual stimulus typically increases the responses of cortical neurons to that stimulus. Because many studies have shown a close relationship between the performance of individual neurons and behavioural performance of animal subjects, it is important to consider how attention affects this relationship. Measurements of behavioural and neuronal performance taken from rhesus monkeys while they performed a motion detection task with two attentional states show that attention alters the relationship between behaviour and neuronal response. Notably, attention affects the relationship differently in different cortical visual areas. This indicates that a close relationship between neuronal and behavioural performance on a given task persists over changes in attentional state only within limited regions of visual cortex.
Functional measurements of human ventral occipital cortex: retinotopy and colour
Authors: Wade Alex R. , Brewer Alyssa A. , Rieger Jochem W. , Wandell Brian A.
Published: September 2002

Human colour vision originates in the cone photoreceptors, whose spatial density peaks in the fovea and declines rapidly into the periphery. For this reason, one expects to find a large representation of the cone–rich fovea in those cortical locations that support colour perception. Human occipital cortex contains several distinct foveal representations including at least two that extend onto the ventral surface: a region thought to be critical for colour vision. To learn more about these ventral signals, we used functional magnetic resonance imaging to identify visual field maps and colour responsivity on the ventral surface. We found a visual map of the complete contralateral hemifield in a 4 cm
2
region adjacent to ventral V3; the foveal representation of this map is confluent with that of areas V1/2/3. Additionally, a distinct foveal representation is present on the ventral surface situated 3–5 cm anterior from the confluent V1/2/3 foveal representations. This organization is not consistent with the definition of area V8, which assumes the presence of a quarter field representation adjacent to V3v. Comparisons of responses to luminance–matched coloured and achromatic patterns show increased activity to the coloured stimuli beginning in area V1 and extending through the new hemifield representation and further anterior in the ventral occipital lobe.
Against memory systems
Authors: Gaffan David
Published: September 2002

The medial temporal lobe is indispensable for normal memory processing in both human and non–human primates, as is shown by the fact that large lesions in it produce a severe impairment in the acquisition of new memories. The widely accepted inference from this observation is that the medial temporal cortex, including the hippocampal, entorhinal and perirhinal cortex, contains a memory system or multiple memory systems, which are specialized for the acquisition and storage of memories. Nevertheless, there are some strong arguments against this idea: medial temporal lesions produce amnesia by disconnecting the entire temporal cortex from neuromodulatory afferents arising in the brainstem and basal forebrain, not by removing cortex; the temporal cortex is essential for perception as well as for memory; and response properties of temporal cortical neurons make it impossible that some kinds of memory trace could be stored in the temporal lobe. All cortex is plastic, and it is possible that the same rules of plasticity apply to all cortical areas; therefore, memory traces are stored in widespread cortical areas rather than in a specialized memory system restricted to the temporal lobe. Among these areas, the prefrontal cortex has an important role in learning and memory, but is best understood as an area with no specialization of function.
Neuronal activity and its links with the perception of multi–stable figures
Authors: Parker Andrew J. , Krug Kristine , Cumming Bruce G.
Published: September 2002

In order to isolate the neuronal activity that relates to the making of perceptual decisions, we have made use of a perceptually ambiguous motion stimulus. This stimulus lies on the boundary between two perceptual categories that correspond to clockwise and counter–clockwise rotation of a three–dimensional figure. It consists of a two–dimensional pattern of moving dots that are capable of generating these two, distinct, three–dimensional percepts. We have studied the responses of neurons in cortical area V5/MT whilst macaque monkeys report judgements about the perceptual configuration of this stimulus. We extract a quantitative statistic called ‘choice probability’ that expresses the covariation of neuronal activity and perceptual choice. An analysis of choice probabilities shows that the pool of neurons involved in the perceptual decisions is a tightly constrained subset of the population of sensory neurons relevant to the perceptual task.
The temporal resolution of neural codes: does response latency have a unique role?
Authors: Oram M. W. , Xiao D. , Dritschel B. , Payne K. R.
Published: September 2002

This article reviews the nature of the neural code in non-human primate cortex and assesses the potential for neurons to carry two or more signals simultaneously. Neurophysiological recordings from visual and motor systems indicate that the evidence for a role for precisely timed spikes relative to other spike times (
ca
. 1–10 ms resolution) is inconclusive. This indicates that the visual system does not carry a signal that identifies whether the responses were elicited when the stimulus was attended or not. Simulations show that the absence of such a signal reduces, but does not eliminate, the increased discrimination between stimuli that are attended compared with when the stimuli are unattended. The increased accuracy asymptotes with increased gain control, indicating limited benefit from increasing attention. The absence of a signal identifying the attentional state under which stimuli were viewed can produce the greatest discrimination between attended and unattended stimuli. Furthermore, the greatest reduction in discrimination errors occurs for a limited range of gain control, again indicating that attention effects are limited. By contrast to precisely timed patterns of spikes where the timing is relative to other spikes, response latency provides a fine temporal resolution signal (
ca
. 10 ms resolution) that carries information that is unavailable from coarse temporal response measures. Changes in response latency and changes in response magnitude can give rise to different predictions for the patterns of reaction times. The predictions are verified, and it is shown that the standard method for distinguishing executive and slave processes is only valid if the representations of interest, as evidenced by the neural code, are known. Overall, the data indicate that the signalling evident in neural signals is restricted to the spike count and the precise times of spikes relative to stimulus onset (response latency). These coding issues have implications for our understanding of cognitive models of attention and the roles of executive and slave systems.
The neural basis of the blood–oxygen–level–dependent functional magnetic resonance imaging signal
Authors: Logothetis Nikos K.
Published: September 2002

Magnetic resonance imaging (MRI) has rapidly become an important tool in clinical medicine and biological research. Its functional variant (functional magnetic resonance imaging; fMRI) is currently the most widely used method for brain mapping and studying the neural basis of human cognition. While the method is widespread, there is insufficient knowledge of the physiological basis of the fMRI signal to interpret the data confidently with respect to neural activity. This paper reviews the basic principles of MRI and fMRI, and subsequently discusses in some detail the relationship between the blood–oxygen–level–dependent (BOLD) fMRI signal and the neural activity elicited during sensory stimulation. To examine this relationship, we conducted the first simultaneous intracortical recordings of neural signals and BOLD responses. Depending on the temporal characteristics of the stimulus, a moderate to strong correlation was found between the neural activity measured with microelectrodes and the BOLD signal averaged over a small area around the microelectrode tips. However, the BOLD signal had significantly higher variability than the neural activity, indicating that human fMRI combined with traditional statistical methods underestimates the reliability of the neuronal activity. To understand the relative contribution of several types of neuronal signals to the haemodynamic response, we compared local field potentials (LFPs), single– and multi–unit activity (MUA) with high spatio–temporal fMRI responses recorded simultaneously in monkey visual cortex. At recording sites characterized by transient responses, only the LFP signal was significantly correlated with the haemodynamic response. Furthermore, the LFPs had the largest magnitude signal and linear systems analysis showed that the LFPs were better than the MUAs at predicting the fMRI responses. These findings, together with an analysis of the neural signals, indicate that the BOLD signal primarily measures the input and processing of neuronal information within a region and not the output signal transmitted to other brain regions.
Introduction
Authors: Parker Andrew , Derrington Andrew , Blakemore Colin
Published: September 2002

About half a century ago, the first micro–electrode recordings of sensory neurons in mammalian visual cortex transformed our thinking about how vision works. Since that time, the physiology of cognitive processes has developed into a mature and complete discipline. New techniques have been developed and the old techniques are being deployed in new ways. However, the most spectacular development has been the growth in the range of topics that are now addressed by this discipline.
The uses of colour vision: behavioural and physiological distinctiveness of colour stimuli
Authors: Derrington Andrew M. , Parker Amanda , Barraclough Nick E. , Easton Alexander , Goodson G. R. , Parker Kris S. , Tinsley Chris J. , Webb Ben S.
Published: September 2002

Colour and greyscale (black and white) pictures look different to us, but it is not clear whether the difference in appearance is a consequence of the way our visual system uses colour signals or a by–product of our experience. In principle, colour images are qualitatively different from greyscale images because they make it possible to use different processing strategies. Colour signals provide important cues for segmenting the image into areas that represent different objects and for linking together areas that represent the same object. If this property of colour signals is exploited in visual processing we would expect colour stimuli to look different, as a class, from greyscale stimuli. We would also expect that adding colour signals to greyscale signals should change the way that those signals are processed. We have investigated these questions in behavioural and in physiological experiments.

We find that male marmosets (all of which are dichromats) rapidly learn to distinguish between colour and greyscale copies of the same images. The discrimination transfers to new image pairs, to new colours and to image pairs in which the colour and greyscale images are spatially different.

We find that, in a proportion of neurons recorded in the marmoset visual cortex, colour–shifts in opposite directions produce similar enhancements of the response to a luminance stimulus.

We conclude that colour is, both behaviourally and physiologically, a distinctive property of images.
Quality in citrus fruit: to degreen or not degreen?
Authors: Poole Nigel D. , Gray Kate
Published: September 2002

The degreening process for citrus accelerates natural colour break which changes fruit from an “unripe” green colour to the characteristically ripe orange/yellow colour. Degreening is used by producers both to extend the citrus season to make short‐term financial gains and to make fruit more attractive to consumers. This study reviews how, in an attempt to improve fruit appearance, other quality attributes may be sacrificed. The process is known to be detrimental to external fruit quality and is also suspected to be detrimental to consumption quality and shelf life. In the context of a dynamic and competitive fruit market, any reduction in product quality and consequent loss consumer satisfaction inevitably will have a negative economic impact on producers and traders. Further technical and marketing research is necessary, but among the conclusions drawn is that there is sufficient evidence already to be cautious about the widespread use of degreening.
The student food shopper
Authors: Ness Mitchell , Gorton Matthew , Kuznesof Sharron
Published: September 2002

Although students have several characteristics in common with the 18‐24 year old youth group, they have many distinguishing features and merit consideration as a separate segment. Yet very little academic research has looked at the student market although over recent years commercial marketers have begun to take more interest in this group. The paper reports the results of a study of student food shopping behaviour. It is concerned especially with establishing the dimensions underlying the importance that students attach to supermarket store attributes, exploring the existence of student segments and subsequently, to profile the segments in terms of shopping behaviour and attitudes to store features. The empirical results indicate that there are four dimensions that underlie the importance of store features. These are defined respectively as economy, finance, products, personnel and access. Subsequently, two clusters are identified. The cluster profiles indicate that the clusters are distinguished by their financial situation.
Women, men and food: the significance of gender for nutritional attitudes and choices
Authors: Beardsworth Alan , Bryman Alan , Keil Teresa , Goode Jackie , Haslam Cheryl , Lancashire Emma
Published: September 2002

This article reports the results of the re‐analysis of a substantial set of survey based quantitative data relating to food beliefs, practices and preferences. The particular focus of attention was upon gender contrasts. Several statistically significant differences between men and women were identified. These differences occurred in such areas as views on food and health, the ethical dimensions of food production and food selection, nutritional attitudes and choices, dietary change, food work and body image. Two distinctive patterns emerged, which the authors termed “virtuous” and “robust”, the former exhibiting attitudes more typical of women, and the latter attitudes more typical of men.
Consumers’ acceptability of organic food in Spain
Authors: Soler Francisco , Gil José M. , Sánchez Mercedes
Published: September 2002

Organic production and its consumption have grown tremendously in recent years. However, in the case of Spain demand still represents only 1 per cent of food expenditure. The main obstacle seems to be that organic food faces problems related to consumers’ acceptability; lack of food availability and seasonality make it difficult to establish appropriate retailing outlets; also, higher costs of production and retailer margins jointly may result in higher prices than consumers are willing to pay for organic food attributes. Research studies have mostly elicited consumers’ willingness‐to‐pay (WTP) for organic food through contingent valuation. Alternatively, explores, using an experimental second‐price sealed‐bid auction, the value that consumers place on organic food and the effect that information included on ecolabel and physical appearance have on their WTP. This methodological approach involves the use of real money and real products, which, in fact, may overcome the hypothetical bias detected in previous studies. Also discusses the effect on WTP of consumers’ demographic characteristics and lifestyles, as well as attitudes towards food safety and buying behaviour. Results show, that as more accurate information is offered, consumers’ acceptability of labelled organic food products increases; and that WTP is highly correlated with consumption habits variables.
Consumer motivations in the purchase of organic food
Authors: Zanoli Raffaele , Naspetti Simona
Published: September 2002

The paper presents partial results from an Italian study on consumer perception and knowledge of organic food and related behaviour. Uses the means‐end chain model to link attributes of products to the needs of consumers. In order to provide insights into consumer motivation in purchasing organic products, 60 respondents were interviewed using “hard” laddering approach to the measurement of means‐end chains. The results (ladders) of these semi‐qualitative interviews are coded, aggregated and presented in a set of hierarchical structured value maps. Even if organic products are perceived as difficult to find and expensive, most consumers judge them positively. All consumers associate organic products with health at different levels of abstraction and want good, tasty and nourishing products, because pleasure and wellbeing are their most important values. Results show that differences exist between groups of consumers with respect to their frequency of use (experience) of organic products and level of information (expertise). Reports and discusses results on consumer cognitive structures at different level of experience.
Organic food consumption
Authors: Vindigni Gabriella , Janssen Marco A. , Jager Wander
Published: September 2002

An approach is introduced to combine survey data with multi‐agent simulation models of consumer behaviour to study the diffusion process of organic food consumption. This methodology is based on rough set theory, which is able to translate survey data into behavioural rules. The topic of rule induction has been extensively investigated in other fields and in particular in learning machine, where several efficient algorithms have been proposed. However, the peculiarity of the rough set approach is that the inconsistencies in a data set about consumer behaviour are not aggregated or corrected since lower and upper approximation are computed. Thus, we expect that rough sets theory is suitable to extract knowledge in the form of rules within a consistent theoretical framework of consumer behaviour.
Are organic food consumers opposed to GM food consumers?
Authors: Verdurme Annelies , Gellynck Xavier , Viaene Jacques
Published: September 2002

The paper aims at investigating whether or not organic food consumers are automatically opposed to genetically modified (GM) food. Results from quantitative market research indicate that this is not the case. Based on attitude towards GM food, three consumer segments are identified: the opponents; the proponents; and the neutrals. Only about 40 per cent of the organic consumers, namely the opponents, reject the use of genetic modification in organic food production. The neutrals are neither against nor in favour of GM food, while the proponents support GM in food production. Besides attitude towards GM food, the proponents differ from the other two segments in terms of beliefs, general attitudes and purchase intentions.
Measuring multiple and single factor technical efficiency in organic farming
Authors: Tzouvelekas Vangelis , Pantzios Christos J. , Fotopoulos Christos
Published: September 2002

Estimates the output‐oriented and input‐specific technical efficiency in two samples of Greek, durum wheat farms – organic and conventional ones – using Kalirajan and Obwona’s stochastic varying coefficient regression model. Findings indicate that the organic wheat farms examined are relatively more efficient. Reasons may include lower profit margins and restrictions on inputs permitted, which may force organic farmers to be more cautious with input use. However, technical efficiency scores are still relatively low for both types of wheat farming. Therefore, considerable scope for cost reducing and farm income improvement may exist in both farming modes. This realization could prove crucial for the long‐run viability and the future course of organic wheat farming.