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From information to action: Working memory mechanisms in the primate brain

Synnöve Carlson

Institute of Biomedicine, Department of Physiology, University of Helsinki, 00014 Helsinki, Finland

Working memory refers to temporaral storage of information that is processed in cognitive tasks. Extracellular single neuron recordings were conducted in the prefrontal cortex (PFC) of trained monkeys to find out 1) whether single neurons respond to visual stimuli presented in depth in front of the monkey and whether such stimuli are used as memoranda in the PFC, 2) whether there is a dissociation between movement- and delay-related neuronal processing in the PFC neurons, and 3) whether single neurons in the posterior cingulate cortex (Pcing), an area richly connected with the PFC and parietal cortex, participate in working memory processing.

In the first study, several neurons in the PFC responded spatially selectively either to ap-proaching or retreating visual stimuli. Furthermore, single neurons fired spatially selectively during the delay period of the delayed response task (DR) in which vi-sual stimuli presented in depth were used as cues. The finding indicates that PFC neurons process visual depth information in the working memory.

In the second study, it was shown that single PFC neurons are tuned for spatial locations, both in oculomotor and manual versions of the DR task. Movement related neu-ronal activity was dissociated: single neurons responded either in relation to the eye or hand movement.

In the third study, neurons in the Pcing responded omni-directionally during the delay period of the DR tasks, which suggests that single neurons in this cortical area do not process mnemonic information but may be involved in attentional monitoring of motor preparation during the task performance.

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