State-Dependent Modulation of Time-Varying Gustatory Responses

Abstract

Sensory processing is modulated by attention, which is a function of network states. Here we show that changes in such states do more than a simple gating of stimuli: they actually re-arrange cortical coding space to emphasize emotional valences. We delivered taste stimuli to rats before and after a spontaneous state change ("disengagement") that is associated with a reduction in attention and a concurrent emergence of cortical mu rhythms. The percentage of cortical neurons that responded to tastes, and the average response across neurons, remained stable with disengagement, but the particulars of the responses changed drastically. The distinctiveness of sucrose and quinine-which represent the high and low ends of the palatability spectrum-increased, the distinctiveness of the two aversive tastes (quinine and citric acid) decreased, and the distinctiveness of sucrose and NaCl, which were almost identically palatable to start with, did not change. Overall, then, the changes appeared to be palatability-specific. Two additional findings were consistent with this conclusion: rats' palatability-related behavioral responses to the tastes changed in similar ways with disengagement and disengagement-related neural changes specifically appeared late in the response, when palatability-specific information emerges in cortical responses. These data suggest that neural state changes can change the content of neural codes.

Learning-Related Plasticity of Temporal Coding in Simultaneously Recorded Amygdala–Cortical Ensembles

“…Responses to saccharin in training sessions were qualitatively similar to those observed previously in our lab: neuron responses typically changed across one or more of three distinct epochs of activity, reflecting somatosensory (taste presence), chemosensory (taste identity), and palatability information sequentially (Katz et al, 2001a;Fontanini and Katz, 2006).…”

“…Almost all of the learningrelated GC plasticity is localized to the time period previously related to palatability processing (Katz et al, 2001a;Fontanini and Katz, 2006). Examination of the subgroup of neurons held across learning confirms that pre-and post-CTA PSTHs are highly similar for the first 0.8 -1.0 s and divergent afterward.…”

“…After this time point, however, their postlearning responses differed markedly from their prelearning responses. The learning-related plasticity shown by neuron 3, meanwhile, began as early as 250 ms after taste stimulation, but even this change continued into later aspects of the response (Katz et al, 2001a;Fontanini and Katz, 2006). Figure 4C shows, for each held GC neuron that was changed by CTA, the time periods of significant pre-post differences (the neurons from Fig.…”

Natural stimuli evoke dynamic sequences of states in sensory cortical ensembles

“…We implanted 32 electrodes into the gustatory cortex (GC) of four attentive rats (28) and recorded bilateral ensemble sensory responses in 13 separate sessions (9.3 neurons per session). By standard analysis, 38% of the neurons were classified as ''taste-responsive'' (Fig.…”

“…Recent evidence indirectly suggests that this possibility may be the case: repeating multineuronal temporal patterns that are not reflected in PSTHs follow application of sensory stimuli (19,20) and precede initiation of motor behaviors (21)(22)(23), although the search algorithms used to identify such patterns are controversial (24,25); furthermore, the speed of perceptual identification itself varies from trial to trial (26,27) in a manner linked to the dynamics of network activity (27)(28)(29)(30).…”