intentional action. However, an additional signal strength analysis revealed that both processes interact with one another. In particular, neural activity within the para- medial frontal cortex was increased for internal as compared to external timing, but only when action selection was speci- ﬁed externally. Combined, these observa- tions challenge the idea of a unitary control system and underscore the existence of distinct, albeit interdependent, decisional processes that together shape voluntary action (Brass and Haggard, 2008). Of note is that this dependency is in accordance with the argument that aspects from the component processes have to be considered in order for an action and its consequences to be evaluated. By introducing an innovative experi- mental paradigm, the work of Krieghoff et al. (2009) has provided a signiﬁcant step into the understanding of intentional control by specifying dissociable brain regions that deal with component func- tions. Further research into the dynamics of voluntary action is necessary in order to detail the functional architecture of intentional behavior and its neural corre- lates. Future studies may elaborate on the inter-regional inﬂuences and coordination of the brain areas that make up the network activity, and the means by which context- related factors modify intentional process- ing within the circuitry. REFERENCES Brass, M., and Haggard, P. (2007). To do or not to do: the neural signature of self-control. J. Neurosci. 27, 9141–9145. Brass, M., and Haggard, P. (2008). The what, when, whether of intentional action. Neuroscientist 14, 319–325. Cunnington,R.,Windischberger,C.,Deecke,L.,andMoser, E. (2002). The preparation and execution of self- initiated and externally-triggered movement: a study of event-related fMRI. Neuroimage 15, 373–385. Cunnington, R., Windischberger, C., Robinson, S., and Moser, E. (2006). The selection of intended actions and the observation of others’actions: a time-resolved fMRI study. Neuroimage 29, 1294–1302. Deiber, M. P., Honda, M., Ibañez, V., Sadato, N., and Hallett, M. (1999). Mesial motor areas in self-initi- ated versus externally triggered movements exam- ined with fMRI: effect of movement type and rate. J. Neurophysiol. 81, 3065–3077. Haggard, P. (2008). Human volition: towards a neuro- science of will. Nat. Rev. Neurosci. 9, 934–946. FRONTIERS COMMENTARY Haggard, P., and Clark, S. (2003). Intentional action: con- scious experience and neural prediction. Conscious Cogn. 12, 695–707. Krieghoff, V., Brass, M., Prinz, W., and Waszak, F. (2009). Dissociating what and when of intentional actions. Front. Hum. Neurosci. 3, 1–10. doi: 10.3389/ neuro.09.003.2009. Lau, H., Rogers, R. D., and Passingham, R. E. (2006). Dissociating response selection and conﬂict in the medial frontal surface. Neuroimage 29, 446–451. Lau,H.C.,Rogers,R.D.,Ramnani,N.,and Passingham,R. E. (2004).Willed action and attention to the selection of action. Neuroimage 21, 1407–1415. Mueller,V.A., Brass, M.,Waszak, F., and Prinz,W. (2007). The role of the preSMA and the rostral cingulate zone in internally selected actions. Neuroimage 37, 1354–1361. Nachev, P., Rees, G., Parton, A., Kennard, C., and Husain, M. (2005). Volition and conﬂict in human medial frontal cortex. Curr. Biol. 15, 122–128. Rushworth, M. F. (2008). Intention, choice, and the medial frontal cortex. Ann. N. Y. Acad. Sci. 1124, 181–207. Received: 31 August 2009; published: 15 May 2010. Citation: Front. Neurosci. (2010) 4, 1: 2–3. doi: 10.3389/ neuro.01.001.2010 Copyright © 2010 Serrien.This is an open-access publication subject to an exclusive license agreement between the authors and the Frontiers Research Foundation, which permits unre- stricted use, distribution, and reproduction in any medium, provided the original authors and source are credited. Forget before you remember: dynamic mechanism of memory decay and retrieval Tatiana Engel* and David Andrieux** Department of Neurobiology and Kavli Institute for Neuroscience,Yale University School of Medicine, New Haven, CT, USA *Correspondence: *tatiana.engel@yale.edu; **david.andrieux@yale.edu A commentary on Neurophysiological bases of exponential sensory decay and top-down memory retrieval: a model by Ariel Zylberberg, Stanislas Dehaene, Gabriel B. Mindlin and Mariano Sigman Sensory systems are confronted with a con- tinuous stream of inputs, but only a small fraction of these sensory stimuli reaches our awareness, is consciously perceived and can be remembered. Perception is never driven solely by the bottom-up stimulation, but crucially depends on the Frontiers in Neuroscience top-down modulations. Top-down signals convey behavioral context, such as atten- tion, expectation and perceptual task, and are reﬂected in the context-speciﬁc response modulation in single neurons (Miller and Cohen, 2001; Corbetta and Shulman, 2002). Top-down interactions can be of many dif- ferent kinds: augmenting or multiplying responses, sharpening tuning curves, con- trolling contextual inﬂuences, or acting as a modulator of plasticity (Desimone and Duncan, 1995; Maunsell and Treue, 2006). Although a lot of empirical knowledge has been accumulated on how top-down inter- actions modulate neural responses, only a few theoretical attempts have been made so far to explain the underlying biophysical mechanisms and to bridge the gap between the behavioral and single-cell data (Buia and Tiesinga, 2006; Deco and Rolls, 2006; Ardid et al., 2007). The recent study by Zylberberg et al. (2009) published in Frontiers in Computational Neuroscience aims to uncover these biophysical mechanisms in a particular setting of top-down memory retrieval. The authors try to answer several general and long-standing questions: How do the bottom-up and top-down signals interact to produce a perception? What are the neural mechanisms of effortless (iconic) vs voluntary (working) memory? May 2010 | Volume 4 | Issue 1 | 3