Posterior parietal cortex represents sensory history and mediates its effects on behaviour

A working memory task in rats demonstrates that the posterior parietal cortex is a critical locus for the representation and use of prior stimulus information. How sensory history affects behaviour Recent sensory experiences, even when irrelevant to the current task at hand, bias memory and perception in humans and monkeys. Carlos Brody and colleagues show that sensory stimulus history also influences the working memory of rats. Silencing the activity of the posterior parietal cortex (PPC), an area previously implicated in working memory, paradoxically improved the rats' performance in a memory and behaviour task—identifying and reporting the loudest of two auditory stimuli. This improvement was due to the selective reduction of the effects of previous sensory stimuli. Electrophysiological recordings showed that PPC neurons carried more information about sensory stimuli of previous trials than about stimuli of the current trial. These findings suggest a role for PPC in maintaining information on recent sensory history. Many models of cognition and of neural computations posit the use and estimation of prior stimulus statistics 1 , 2 , 3 , 4 : it has long been known that working memory and perception are strongly impacted by previous sensory experience, even when that sensory history is not relevant to the current task at hand. Nevertheless, the neural mechanisms and regions of the brain that are necessary for computing and using such prior experience are unknown. Here we report that the posterior parietal cortex (PPC) is a critical locus for the representation and use of prior stimulus information. We trained rats in an auditory parametric working memory task, and found that they displayed substantial and readily quantifiable behavioural effects of sensory-stimulus history, similar to those observed in humans 5 , 6 and monkeys 7 . Earlier proposals that the PPC supports working memory 8 , 9 predict that optogenetic silencing of this region would impair behaviour in our working memory task. Contrary to this prediction, we found that silencing the PPC significantly improved performance. Quantitative analyses of behaviour revealed that this improvement was due to the selective reduction of the effects of prior sensory stimuli. Electrophysiological recordings showed that PPC neurons carried far more information about the sensory stimuli of previous trials than about the stimuli of the current trial. Furthermore, for a given rat, the more information about prev