# Editorial overview: Systems neuroscience

Michael Long, Rosa Cossart

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Michael Long, Rosa Cossart. Editorial overview: Systems neuroscience. Current Opinion in Neurobiology, 2018, 52, pp.iv-vi. 10.1016/j.conb.2018.08.011. hal-01963553

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Current Opinion in
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# Editorial overview: Systems neuroscience

Michael Long and Rosa Cossart

**Current Opinion in Neurobiology** 2018, 52:iv–vi

For a complete overview see the [issue](http://dx.doi.org/10.1016/j.conb.2018.08.011)

0959-4388/© 2018 Published by Elsevier Ltd.

Michael Long

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NYC School of Medicine, USA
e-mail: Michael.Long@nyumc.org

Michael Long is an associate professor in the Neuroscience Institute at the NYU School of Medicine. He completed his graduate studies with Barry Connors (Brown University) and his postdoctoral work with Michale Fee (MIT). His laboratory studies the neural circuits that underlie skilled movements, often in the service of vocal interactions. To accomplish this, he has taken a comparative approach, examining relevant cellular and network mechanisms in the songbird, the rodent, and the human.

Rosa Cossart

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Institute of Mediterranean Neurobiology
(INMED), INMED, INSERM UMR1249, Aix-
Marseille University, Parc Scientifique de
Luminy BP.13, 13273 Marseille cedex 09,
France
e-mail: rosa.cossart@inserm.fr

Rosa Cossart is the new Director of the
Institute of Mediterranean Neurobiology
(INMED), affiliated to INSERM and

Systems neuroscience classically studies how neuronal circuits dynamically interact at varying spatial and temporal scales to process sensory information, represent the external environment to guide decision making, and execute movements. A recent explosion of techniques for studying neural dynamics has revolutionized this discipline and therefore our understanding of brain function. Indeed, these tools have provided unprecedented observations of neural activity and elegant means of manipulating specific components of these circuits, albeit in a more consolidated number of animal models. Such approaches have enabled systems neuroscientists to go beyond the description of reflexive behaviors or of the first stages of sensory processing, opening the way for the understanding of how cognitive processes such as memory are implemented at the level of large scale interacting circuits to support adaptive behavior.

This volume of *Current Opinion in Neurobiology* provides a snapshot of the state of this field with an emphasis on the contextual modulation of multisensory processing, on memory circuits, or on the development of long-range interacting networks. It also offers an overview of recent methodological advances and new animal models with an emphasis on a meso-circuit level of description.

Perhaps the most rapidly maturing aspect of neuroscience is our ability to measure the activity of large neural ensembles in action. For instance, in the olfactory bulb, Chong and Rinberg use imaging methods capable of monitoring complex spatiotemporal patterns of activity during the performance of odor-guided behaviors and examine ways in which such activity can be experimentally manipulated or even recapitulated in order to test the importance of such codes. In their review, Pakan et al. discuss how the recent development of genetic tools and imaging techniques has led to the urgent need to standardize experimental conditions and analysis methods.

Sensory processing represents the most commonly studied aspect of systems neuroscience. Although other sensory modalities, such as vision, may receive more experimental attention, tremendous progress is being made in other sensory systems as well. In his contribution, Gu explores the primate vestibular network, focusing on a substantial cortical representation that enables the perception of self-motion and spatial orientation. Additionally, Bokiniec et al. examine the circuitry underlying the perception of innocuous thermal stimuli and highlight recent advances that address the functional organization of networks underlying the processing of skin surface temperature.

How "non-sensory" signals (arousal, experience, prediction, attention, social context, etc.) affect the processing of sensory inputs is an important and
Aix-Marseille University, a pioneering
Institute in the field of Systems
Developmental Neuroscience. After
graduating in Mathematics and Physics from
the Ecole Centrale Paris, she studied the
functional rewiring of GABAergic circuits in
epilepsy during her PhD with Drs. Bernard
and Ben-Ari. As a postdoctoral fellow with Pr.
Yuste at Columbia University, she pioneered
the use of calcium imaging to study cortical
circuit function. Her lab made seminal
contributions to the understanding of how
development scaffolds hippocampal circuits.
They discovered “hub cells” and more
recently “assemblies” forming the functional
building blocks of hippocampal function.

timely topic and a recent matter of debate. The issue of “contextual
modulation”, when a primary feedforward input interacts with modulatory
influences arising from top-down networks is therefore becoming a central
focus in systems neuroscience. Pakan *et al.* discuss the impact of these ‘non-
sensory’ variables, such as state-dependent and experience-dependent
modulation of visual processing, implicating both corticocortical and thala-
mocortical pathways as well as neuromodulation. *Khan and Hofer* explore
how such information enables bottom-up and top-down influences to be
integrated in order to form predictions about the visual world. *Batista-Brito
et al.* examine the microcircuitry that enables these contextual influences to
be implemented in neocortex and focus on the role of inhibitory interneur-
ons and neuromodulation in both normal and pathological brain processing.
*Kuchibhotla and Bathellier* demonstrate the importance of such contextual
use for adding perceptual richness to the auditory cortex and shaping
behavioral responses.

Although brain state can influence sensory perception, individual sensory
streams (e.g., olfaction) often have a significant impact on ongoing brain
function. Choi *et al.* review the processes underlying the integration of
sensory information from multiple modalities, focusing on the dynamic
modulation of these factors and the importance of this process on perception.
Robbe examines the integration of sensory signals with motor information
within the striatum and argues that the somatotopic organization may
facilitate motor learning. Ben-Tov *et al.* use the archerfish, which can
integrate sophisticated visual information to localize and target prey, to
examine dynamic sensorimotor processes underlying an ethologically rele-
vant behavior. Knafo and Wyart use advanced optical methods to identify
the cell types involved in mechanosensory feedback in the larval zebrafish
that are engaged in active locomotion.

Although thalamocortical inputs to sensory structures have been traditionally
thought to simply relay afferent information to the neocortex, several lines of
evidence suggest that the thalamus may be carrying out a diverse set of
functions. For example, Gent and Adamantidis discusses recent findings that
implicate the thalamus in the regulation of sleep-wake states, expanding the
view that such arousal states are primarily determined by brainstem struc-
tures. Antón-Bolaños *et al.* explore the role of extrinsic versus intrinsic factors
in the establishment of functional networks during development, with a focus
on the early dialogue between thalamic nuclei and sensory cortices, and
Colonnese and Phillips examine the changes in inhibitory cell types that may
enable the developmental switch from “pre-sensory” early thalamocortical
coordinated activity to high resolution sensory processing.

Systems developmental neuroscience, an emerging subdiscipline at the
interface between development and systems neuroscience is particularly
well-represented by several reviews in this special issue including the two
cited above. In that respect, the review by Valero and Menendez de la Prida
exemplifies how much development may shape the functional structure of
adult memory circuits. Indeed, it reviews recent evidence indicating a
segregation between temporal and contextual information flows along the
radial axis of the CA1 hippocampal region, an emergent outcome structure of
development. This issue includes several additional reviews related to the
systems neuroscience of cognition. Piskorowski and Chevaleyre highlight
the critical role of CA2 in memory circuits, not only for social behavior but
also regarding spatial information. They argue that CA2 may act as a conflict
detector, comparing contextual information with internal representation.
Mably and Colgin discusses how gamma oscillatory activity is involved in
memory processes, providing a window into the brains
interworkings in health and disease and potentially a
means for novel therapeutic interventions. The hippo-
campus and related structures have long been known to
play a role in spatial navigation, and Maimon and Green
use the drosophila as a model system to study the
computational similarities that exist between insect and
mammalian head direction systems to enrich existing
models for the circuitry that provides directional infor-
mation for such behaviors.

Another advantage of modern techniques is the ability to
examine the impact of long-range connectivity. A pair of
reviews explore the importance of a specific interconnec-
tion, linking the prefrontal cortex to the amygdala, for two
distinct brain processes. Yizhar and Klavir examine these
interactions in the context of establishing and modifying
associations between a cue and an outcome in the service
of adaptive and maladaptive learning, while Rozeske and
Herry link the connections between these structures to
the rapid and flexible expression of fear behavior.

Movement is the final outcome of nervous system func-
tion. Muscatelli and Bouret review recent literature
regarding a highly important innate behavior, namely
the suckling reflex that must be initiated immediately
after birth and is influenced by hypothalamic circuits that
regulate feeding. Aranha and Vasconcelos examine
female innate behaviors in the drosophila, specifically
courtship responses and egg-laying decisions. For skilled
behaviors, Yoshida and Isa present comparative results
from rodents and primates focusing on the role of the
corticomotorneuronal pathway in enabling dexterous
hand movements.

Despite the impressive progress in systems neurosci-
ence in recent years, many aspects of brain function
remain poorly understood. For instance, although an
enormous amount of effort within the field is presently
being directed towards simple model organisms, Bansal
et al. tackle the complexity of the human brain by
developing personalized models constrained by anatom-
ical and functional data, providing a means for querying
the human brain function through ‘virtual experiments’
as well as a potentially powerful new tool for neurosur-
gical applications. Another potential gap in our knowl-
edge is rooted in the paucity of circuit-oriented studies
that focus on social neuroscience. Brecht et al. address
existing literature, highlighting differences in sensory
processing based on social context and address sexually
dimorphic aspects of nervous system function as early
steps towards establishing a mechanistic understanding
of the social brain.

Collectively, these reviews reveal how much systems
neuroscience is experiencing an exciting period sup-
ported by unprecedented technological breakthroughs.
It is by essence an interdisciplinary field which is in turn
currently giving rise to the emergence of new subfields,
such as ‘systems developmental neuroscience’ or
‘systems social neuroscience’. In the close future, systems
neuroscientists throughout these various subfields will
certainly need to work hand in hand with data and
computational neuroscientists to standardize their experi-
ments and analysis and bridge the gap between data and
understanding.

**Conflict of interest statement**

Nothing declared.