Abstract
Variability in cortical neural activity potentially limits sensory discriminations. Theoretical work shows that information required to discriminate two similar stimuli is limited by the correlation structure of cortical variability. We investigated these information-limiting correlations by recording simultaneously from visual cortical areas primary visual cortex (V1) and extrastriate area V4 in macaque monkeys performing a binocular, stereo depth discrimination task. Within both areas, noise correlations on a rapid temporal scale (20-30 ms) were stronger for neuron pairs with similar selectivity for binocular depth, meaning that these correlations potentially limit information for making the discrimination. Between-area correlations (V1 to V4) were different, being weaker for neuron pairs with similar tuning and having a slower temporal scale (100+ ms). Fluctuations in these information-limiting correlations just prior to the detection event were associated with changes in behavioral accuracy. Although these correlations limit the recovery of information about sensory targets, their impact may be curtailed by integrative processing of signals across multiple brain areas.NEW & NOTEWORTHY Correlated noise reduces the stimulus information in visual cortical neurons during experimental performance of binocular depth discriminations. The temporal scale of these correlations is important. Rapid (20-30 ms) correlations reduce information within and between areas V1 and V4, whereas slow (>100 ms) correlations between areas do not. Separate cortical areas appear to act together to maintain signal fidelity. Rapid correlations reduce the neuronal signal difference between stimuli and adversely affect perceptual discrimination.
Highlights
Processing in the sensory areas of cerebral cortex is thought to limit the detection and discrimination of weak sensory signals [1]
We trained two rhesus macaques (M. mulatta) to observe four patches of dynamic random dot stereograms (RDSs) and perform an odd-one-out task (Fig. 1), in which they detected which one of the four patches displayed a change in binocular depth
The monkeys’ behavior indicated attention to the RDS stimuli in the Present RDS phase, as they were better at reporting the location of the disparity step change as it grew in magnitude (Fig. 1B, % correct), while their reaction times (RTs) decreased
Summary
Processing in the sensory areas of cerebral cortex is thought to limit the detection and discrimination of weak sensory signals [1]. Initial work examined how the changes in the firing of action potentials induced by near-threshold changes in the sensory stimulus could be detected against the variability of the base level of cortical activity [2,3,4,5]. This work elucidated how detection and discrimination could be related to the statistics of the firing of single neurons. These initial studies indicated that it was not unusual for the detection performance of single neurons to match the behavioral performance of the entire visual system. Since the firing of all neurons shows some variability, combination of the firing from a pool of neurons to form a multineuron sensory signal ought to improve the detection rate for weak stimuli. The puzzle is why the nervous system apparently cannot provide a better sensitivity for the organism by making a statistical combination of the signals from multiple neurons
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