Frontoparietal Circuitry Underlying Saccade Control in the Common Marmoset
Abstract
Our visual world is full of far more stimuli than can be processed simultaneously. Yet we are able to efficiently extract behaviourally relevant information from a scene, primarily by performing rapid saccadic eye movements. These processes are under the control the frontoparietal network, two critical nodes of which are: the lateral intraparietal area (LIP) and the frontal eye fields (FEF). Extensive research in the macaque has causally implicated these areas in visual attention and oculomotor control. However, the organization of the activity of single neurons in these areas across cortical layers remains poorly understood as these regions are deep within sulci in the macaque. The marmoset, with a lissencephalic cortex, largely homologous frontoparietal network, and comparable oculomotor repertoire, presents a unique opportunity to address these questions. First, the homology of these cortical areas must be established. Recent work from our group supports marmoset LIP homology, however, FEF remains to be explored. The first aim of this dissertation was identify and characterize marmoset FEF. Using intracortical microstimulation (ICMS), we restricted marmoset FEF to areas 8a, 45, 6D and 8C, and demonstrated frontal cortical organization consistent with other primates, supporting the use of marmosets for neurophysiological investigations of oculomotor control and attention. The subsequent aims of this work were to examine the laminar dynamics of LIP and FEF in marmosets completing a target selection task. We observed neurons in both LIP and FEF involved in target selection, with FEF showing a stronger link to motor control. Interestingly, organization in LIP followed the canonical circuit model (CCM), with input in the granular, target selection in supragranular, and output in infragranular layers. In contrast, FEF displayed a unique bilaminar visual input in superficial layers and target selection in deeper layers, resembling recent observations in other frontal areas more than the traditional CCM. These findings suggest that while models developed in primary sensory areas might apply to some regions of association cortex, their generalizability to frontal areas is limited. This work underscores the marmoset’s value as a model for studying attention and cognition, and broadens our knowledge of cortical organization underlying these phenomena.