| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Editorial Focus
). The researchers go on to suggest that temporal codes for taste probably have little to do with now-classic notions such as synchrony but rather that precise spike times are stochastic and empty of information. Thus their results have implications for the way we think about both gustation and temporal coding in general.
The technical difficulty of taste experiments—the challenge of controlling a turbulent stimulus flow, the long waits for activity to return to baseline (Katz et al. 2001)— have for the most part deprived taste researchers of the statistical power necessary to bring analyses of time course to bear on electrophysiology. What Di Lorenzo and Victor have done is, at its root, simple. They have killed the size of the stimulus array in favor of multiple trial presentations, while recording from the nucleus of the solitary tract (NST), the first brain stem taste relay. This has allowed them to show the trial-to-trial response variability and thus to reveal that for some neurons the overall response magnitude—the currency of both LL and ANP codes—was an unreliable indicator of taste identity. Even when this was not the case, however, further information theoretic analyses revealed that the time course of activity was frequently more information-rich than was the overall response magnitude. Their analysis compared the "costs" of transforming a single trial response to a particular tastant (say, Na) to a different single trial response, either that of another Na trial or that of a response to a different taste (say, quinine). A higher cost means more difference between spike trains and thus more taste-specific information. The analysis could be varied with regard to how much the incurred cost depended on moving spikes around as opposed to simply adding or removing spikes (equivalent to testing the importance of overall response magnitude).
Di Lorenzo and Victor found that, for more than half of their sample of NST neurons, spike trains for different tastants were more distinguishable when temporal patterns were taken into account then when they were not. That is, the time courses of NST responses contained taste-specific information. Furthermore, the importance of the temporal pattern had a limited precision—moving spikes less than 250 ms often had little impact—and varying the cost of changing the sizes of particular intervals between spikes (a manipulation that lengthened or shortened the entire train) made little difference compared with changing rates within the same length of time. These facts make it likely that the population temporal code has little to do with the occurrence of synchronous or precisely timed spikes, a finding that is consistent with recent analyses of multi-neuron responses in taste cortex (Katz et al. 2002b), and that makes this paper an important new addition to the evolving debate over the nature of temporal codes in the nervous system (see Baker and Lemon 2000; Gutig et al. 2002; Oram et al. 1999; Shadlen and Newsome 1998). Simply put, the temporal codes observed here cannot be decoded by classic coincidence detectors.
This paper joins a small but growing literature suggesting that taste processing is more complex and dynamic than has previously been assumed (for review, see Katz et al. 2002a) and goes beyond previous work by examining, in finer detail, how time may work in taste coding. Given the increasing ubiquity with which temporal coding is reported in studies of sensory physiology (for review, see Ghazanfar and Nicolelis 2000) and the fact that notions similar to LL and ANP thrive across neuroscience, the findings of Di Lorenzo and Victor should be on the reading list of any systems neuroscientist studying sensation and perception.
Department of Psychology and Volen National Center for Complex Systems, Brandeis University, Waltham, Massachusetts 02454-9110
Address reprint requests to D. B. Katz (E-mail: dbkatz{at}brandeis.edu).
REFERENCES
Baker SN and Lemon RN. Precise spatiotemporal repeating patterns in monkey primary and supplementary motor areas occur at chance levels. J Neurophysiol 84: 1770–1780, 2000.
Di Lorenzo PM and Victor JD. Taste response variability and temporal coding in the nucleus of the solitary tract of the rat. J Neurophysiol 90: 1418–1431, 2003.
Ghazanfar AA and Nicolelis MAL. The space-time continuum in mammalian sensory pathways. In: Time and the Brain, edited by Miller R. Sidney, Australia: Harwood, 2000, p. 97–130.
Gutig R, Aertsen A, and Rotter S. Statistical significance of coincident spikes: count-based versus rate-based statistics. Neural Comput 14: 121–153, 2002.
Katz DB, Nicolelis MA, and Simon SA. Gustatory processing is dynamic and distributed. Curr Opin Neurobiol 12: 448–454, 2002a.[ISI][Medline]
Katz DB, Simon SA, and Nicolelis MA. Taste-specific neuronal ensembles in the gustatory cortex of awake rats. J Neurosci 22: 1850–1857, 2002b.
Katz DB, Simon SA, and Nicolelis MAL. Electrophysiological studies of gustation in awake rats. In: Methods and Frontiers in the Chemical Senses, edited by Simon SA and Nicolelis MAL. Boca Raton, FL: CRC, 2001, p. 339–357.
Oram MW, Wiener MC, Lestienne R, and Richmond BJ. Stochastic nature of precisely timed spike patterns in visual system neuronal responses. J Neurophysiol 81: 3021–3033, 1999.
Shadlen MN and Newsome WT. The variable discharge of cortical neurons: implications for connectivity, computation, and information coding. J Neurosci 18: 3870–3896, 1998.
This article has been cited by other articles:
|
|
 |
|
  J. R. Stapleton, M. L. Lavine, R. L. Wolpert, M. A. L. Nicolelis, and S. A. Simon Rapid Taste Responses in the Gustatory Cortex during Licking J. Neurosci., April 12, 2006; 26(15): 4126 - 4138. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C.Y. Chan, J.E. Yoo, and S.P. Travers Diverse Bitter Stimuli Elicit Highly Similar Patterns of Fos-like Immunoreactivity in the Nucleus of the Solitary Tract Chem Senses, September 1, 2004; 29(7): 573 - 581. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
