Dataset Information

Trial-to-trial variability of the prefrontal neurons reveals the nature of their engagement in a motion discrimination task.

ABSTRACT: During motion discrimination tasks, many prefrontal cortex (PFC) neurons are strongly modulated by the behavioral context, suggesting their involvement in sensory discriminations. Recent studies suggest that trial-to-trial variability of spiking activity characteristic of cortical neurons could be a source of information about the state of neurons and their participation in behavioral tasks. We tested this hypothesis by examining the variability of putative pyramidal PFC neurons, a likely source of top-down influences. The variability of these neurons was calculated as a ratio of spike count variance to its mean (fano factor, FF), while monkeys compared the directions of two moving stimuli, sample and test, separated by a delay. We found that the FF tracked consecutive components of the task, dropping rapidly with the onset of stimuli being discriminated and declining more slowly before each salient event of the trial: The sample, the test, and the response. These time-dependent signals were less consistent in direction selective neurons and were largely absent during passive fixation. Furthermore, neurons with test responses that reflected the remembered sample decreased their FF well before the test, revealing the predictive nature of response variability, an effect present only during the active task. The FF was also sensitive to behavioral performance, exhibiting different temporal dynamics on error trials. These changes did not depend on firing rates and were often the only metric correlated with task demands. Our results demonstrate that trial-to-trial variability provides a sensitive measure of the engagement of putative pyramidal PFC neurons in circuits subserving discrimination tasks.

SUBMITTER: Hussar C

PROVIDER: S-EPMC3003075 | biostudies-literature | 2010 Dec

REPOSITORIES: biostudies-literature

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Trial-to-trial variability of the prefrontal neurons reveals the nature of their engagement in a motion discrimination task.

Hussar Cory C Pasternak Tatiana T

Proceedings of the National Academy of Sciences of the United States of America 20101122 50

During motion discrimination tasks, many prefrontal cortex (PFC) neurons are strongly modulated by the behavioral context, suggesting their involvement in sensory discriminations. Recent studies suggest that trial-to-trial variability of spiking activity characteristic of cortical neurons could be a source of information about the state of neurons and their participation in behavioral tasks. We tested this hypothesis by examining the variability of putative pyramidal PFC neurons, a likely source ...[more]

PMID: 21098286

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Project description:Pupillometry, the measure of pupil size and reactivity, has been widely used to assess cognitive processes. Changes in pupil size have been shown to correlate with various behavioral states, both externally and internally induced such as locomotion, arousal, cortical state, and decision-making processes. Besides, these pupillary responses have also been linked to the activity of neuromodulatory systems that modulate attention and perception such as the noradrenergic and cholinergic systems. Due to the extent of processes the pupil reflects, we aimed at further resolving pupillary responses in the context of behavioral state and task performance while recording pupillary transients of mice performing a vibrotactile two-alternative forced-choice task (2-AFC). We show that before the presentation of task-relevant information, pre-stimulus, pupil size differentiates between states of disengagement from task performance vs. engagement. Also, when subjects have to attend to task stimuli to attain a reward, post-stimulus, pupillary dilations exhibit a difference between correct and error responses with this difference reflecting an internal decision variable. We hypothesize that this internal decision variable relates to response confidence, the internal perception of the confidence the subject has in its choice. As opposed to this, we show that in a condition of passive performance, when the stimulus has no more task relevance due to reward being provided automatically, pupillary dilations reflect the occurrence of stimulation and reward provision but not decisional variables as under active performance. Our results provide evidence that in addition to reflecting attentiveness under task performance rather than arousal per se, pupil dilations also reflect the confidence of the subject in his ensuing response. This confidence coding is overlaid within a more pronounced pupil dilation that reflects post-decision components that are related to the response itself but not to the decision. We also provide evidence as to how different behavioral states, imposed by task demands, modulate what the pupil is reflecting, presumably showing what the underlying cognitive network is coding for.

Dataset Information

Trial-to-trial variability of the prefrontal neurons reveals the nature of their engagement in a motion discrimination task.

Publications

Trial-to-trial variability of the prefrontal neurons reveals the nature of their engagement in a motion discrimination task.

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