Neural correlates of a postponed decision report

Abstract

Depending on environmental demands, a decision based on a sensory evaluation may be either immediately reported or postponed for later report. If postponed, the decision must be held in memory. But what exactly is stored by the underlying memory circuits, the final decision itself or the sensory information that led to it? Here, we report that, during a postponed decision report period, the activity of medial premotor cortex neurons encodes both the result of the sensory evaluation that corresponds to the monkey's possible choices and past sensory information on which the decision is based. These responses could switch back and forth with remarkable flexibility across the postponed decision report period. Moreover, these responses covaried with the animal's decision report. We propose that maintaining in working memory the original stimulus information on which the decision is based could serve to continuously update the postponed decision report in this task.medial premotor cortex ͉ monkeys ͉ sensory discrimination ͉ working memory S tudies in behaving monkeys that combine psychophysical and neurophysiological experiments have provided new insights into how a neural representation of a sensory stimulus relates to perception (1-8), memory (9-12), and decision making (13-19). In particular, there has been important progress regarding the neural codes associated with these cognitive functions in the visual and somatic modality (20,21). The basic philosophy of this approach has been to investigate these cognitive functions by using highly simplified stimuli, so that diverse subcortical and cortical areas can be studied during the same behavior.In the task we previously used, monkeys report whether the second stimulus frequency (f2) is higher or lower than the first stimulus frequency (f1) (22). This cognitive operation requires that subjects compare information of f1 temporally stored in working memory to the current information of f2 to form a decision of whether f2 Ͼ f1 or f2 Ͻ f1, and to immediately report the outcome by pressing one of two push buttons. We found that the activity of the recorded neurons of several cortical areas encodes f1 in a monotonic firing rate code beginning in the primary somatosensory cortex (5-7), continuing in the secondary somatosensory cortex (5), the ventral premotor cortex (19), the prefrontal cortex (10), and the medial premotor cortex (MPc) (18). Except for the primary somatosensory cortex, these cortical areas encode information of f1 during the delay period between f1 and f2 (5,10,11,(17)(18)(19). During presentation of f2, some neurons of all these cortical areas respond to f2, but some other neurons reflect past information of f1, or of the difference between f2 and f1, and generate a differential response consistent with the decision motor report (17)(18)(19). In this chain of neural processes, the primary motor cortex becomes engaged only during the motor report period (19,21). These results showed that the stimulus parameters of f1 and f2 and their interactions can be dec...

Neural encoding of auditory discrimination in ventral premotor cortex

“…Again, these responses occurred at different times. These responses are very similar to those observed in medial premotor cortex during the postponed decision report period, while monkeys executed the vibrotactile discrimination task (16). Thus, during the postponed decision report period, the dynamics of the neuronal population of VPC holds in line all of the elements associated with task execution.…”

“…ROC index was calculated using methods from signal detection theory (13,14,16,34). This quantity measures the overlap between two response distributions, in this case between hits and errors for each (f1, f2) pair.…”

“…For this, we sorted the responses into hits and errors and calculated a choice probability index (13,14,16,34). This quantified for each (f1, f2) pair whether responses during error trials were different from responses during correct trials.…”

“…The contribution of sensory cortices in this cognitive operation has been investigated before, but the results suggest that they are primarily associated with stimulus encoding (4)(5)(6)(7)(8)(9). In contrast, those cortical areas that receive inputs from sensory and memory circuits, and send outputs to the motor circuits appear well suited for elaborating perceptual decisions (10)(11)(12)(13)(14)(15)(16). For example, the ventral premotor cortex (VPC) receives projections from sensory areas of the parietal and temporal lobes (17)(18)(19) and association areas of the prefrontal cortex (20), and it sends projections to motor areas of the frontal lobe (18), subcortical structures (21) and spinal cord (22,23).…”

Coherent delta-band oscillations between cortical areas correlate with decision making

“…The paradigm used here has been described (34,35). The monkey sat on a primate chair with its head fixed in an isolated, soundproof room.…”