Inactivation of lateral prefrontal cortex increases activity of MT neurons during memory-guided comparisons of visual motion

[摘要] It is widely accepted that lateral prefrontal cortex (LPFC) is a likely source of top-down influences on neurons processing sensory information. Although the details of top-down connectivity from the LPFC to motion processing area MT remain to be worked out, the existing anatomy suggests that the direct inputs to MT originate in the more ventral prearcuate region of the LPFC (8Av), while the dorsal portion (8Ad, 46) sends direct inputs to the parietal cortex (Petrides & Pandya, 2006). Despite the difference in their targets, the two sub-regions show similarities in the behavior of their neurons during memory-guided motion comparisons, displaying direction selective activity indicative of the bottom-up signals arising in MT (Zaksas & Pasternak, 2006). We examined the functional parcellation of the top-down influences of the LPFC by recording activity in MT before and after inactivating sub-regions within the LPFC, while monkeys compared directions of two moving random-dot stimuli, separated by a delay. Inactivation of the dorsal sub-region resulted in dramatic increases in the firing rates of the majority of recorded neurons throughout the entire trial, but no measurable effects on behavioral performance, largely intact tuning for motion direction and preserved anticipatory modulation of delay activity. In response to motion, the upward shift in mean activity was accompanied by a proportional increase in variance, suggesting additive increase in gain indicative of a shift in the operational regime of neuronal circuits within MT. This non-specific disinhibition involving the majority of MT neurons following LPFC inactivation is consistent with the operation of the Inhibitory Stabilizing Network model which provides a powerful account for the balance between excitation and inhibition in cortical networks (Rubin et al, 2015). Ongoing inactivation involving the ventral portions (8Av) of LPFC will reveal whether different sub-regions within the LPFC give rise to different types of top-down influences.

[学科分类] 眼科学