A canonical microcircuitry for visuomotor transformations in the primate brain

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In order to perform goal oriented actions, the brain must map sensory signals conveying information about the position of objects in space into motor commands for the muscles that ultimately execute actions. In primates, previous studies have identified a complex circuit for transforming visual signals into a specific type of motor action, gaze shifts toward objects in space. Several studies have found neurons that encode visual signals, neurons that encode movement goals (gaze shifts), as well as neurons that encode a mix of the two signals across several brain areas of the so called oculomotor network, lateral intraparietal (LIP), Frontal Eye Fields (FEF), Supplementary Eye Fields (SEF) and more recently area 8A, anterior to the FEF. The overarching goal of the proposal is to reveal the details of the brain circuit underlying this visuomotor transformation. We hypothesize that visuomotor transformation for gaze occurs serially in different brain areas of the oculomotor network, and that the transformation is governed by two basic principles of cortical organization: a) vertical processing within cortical columns that span the thickness of the gray matter following a unidirectional bias (from upper layers to lower layers: visual to motor), and b) horizontal processing between neighboring columns mainly within superficial cortical layers (II and III). We further hypothesize that horizontal processing is mediated by groups of excitatory pyramidal neurons that interact via inhibitory interneurons (e.g., Parvalbumin cells). Such dynamics is key for selecting a target for a gaze shift when multiple stimuli are available. The output of these computations is then passed to the infragranular layers (V-VI) where pyramidal neurons send the “motor” commands to the next processing stage (e.g., cortical area downstream or the Superior Colliculus). We will test this hypothesis by recording the responses of neurons in different cortical layer of areas LIP and FEF of common marmosets (challitrix jacchus) performing tasks that require transforming visual signals into gaze commands. We will use linear probes consisting of multiple contacts that span the entire depth of the cortex implanted via brain navigation techniques and determine how visuomotor processing within cortical columns, between cortical columns and across different areas take place. The results will reveal the circuitry and mechanisms of the visuomotor transformation for gaze in the primate brain.