Time dependent involvement of Posterior Parietal and Prefrontal cortex in a rat auditory parametric working memory task

AthenaTalk: Time dependent involvement of Posterior Parietal and Prefrontal cortex in a rat auditory parametric working memory task

Speaker: Dr Athena Akrami – Brodylab, Princeton University, US

May 26th 2015 – 4.00 pm

Cesare Musatti Room – School of Psychology – University of Padova

Via Venezia, 8 – PADOVA

 

Abstract

Working memory (WM) refers to the ability to store and manipulate information across time intervals of a few seconds. A particular example of working memory task is the sequential comparison of two graded stimuli separated by a delay period of a few seconds, which forces the subject to maintain an analog value in memory. This form of WM is called Parametric Working Memory (PWM) and its neural correlates have been studied in primates (Romo and Salinas 2003). The prefrontal and posterior parietal cortices (mPFC and PPC) have been proposed to be involved in working memory (Pasternak and Greenlee 2005, Harvey et. al 2012), but no inactivation experiments probing whether these areas are necessary for parametric working memory have been performed. Moreover, it remains unknown whether the involvement of these brain regions is affected by memory retention time. We have developed an auditory delayed comparison task in rats, adapted from a tactile task (Fassihi and Akrami et. al 2014). In this task, rats compare two sequential auditory stimuli, ‘f1’ and ‘f2’, separated by a variable delay. Stimuli consist of broadband noise (2K-20K Hz), generated as a series of Sound Pressure Level (SPL) values sampled from a zero-mean normal distribution. Rats should judge which of f1 and f2 had greater SPL standard deviation. Training steps were formalized into semi-automated computer code, requiring minimal human intervention. Rats show a remarkable ability to hold information about f1 stimulus in their memory for up to 10s (the longest tested). For the first time we carry out local reversible inactivations of cortical regions to probe their role in PWM and we show that inactivations of either PPC or mPFC impact behavior. Interestingly, only PPC inactivation leads to delay-duration dependent impairment. To precisely chart PPC involvement, we optogenetically silenced it, using halorhodopsin (eNpHR3.0), during different time points of the trial. Using a logistic regression model to analyze the specific task components impacted by inactivations, together with electrophysiological recordings, our data suggest distinct roles played by PPC and mPFC in auditory PWM.

 

Local organizer: Organizers: Antonino Vallesi and Vincenza Tarantino

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