Visual Cortical Area MT Is Required for Development of the Dorsal Stream and Associated Visuomotor Behaviors.

The middle temporal (MT) area of the extrastriate visual cortex has long been studied in adulthood for its distinctive physiological properties and function as a part of the dorsal stream, yet interestingly it possesses a similar maturation profile as the primary visual cortex (V1). Here, we examined whether an early-life lesion in MT of marmoset monkeys (six female, two male) altered the dorsal stream development and the behavioral precision of reaching-to-grasp sequences. We observed permanent changes in the anatomy of cortices associated with both reaching (parietal and medial intraparietal areas) and grasping (anterior intraparietal area), as well as in reaching-and-grasping behaviors. In addition, we observed a significant impact on the anatomy of V1 and the direction sensitivity of V1 neurons in the lesion projection zone. These findings indicate that area MT is a crucial node in the development of primate vision, affecting both V1 and areas in the dorsal visual pathway known to mediate visually guided manual behaviors.SIGNIFICANCE STATEMENT Previous studies have identified a role for the MT area of the visual cortex in perceiving motion, yet none have examined its central role in the development of the visual cortex and in the establishment of visuomotor behaviors. To address this, we used a unilateral MT lesion model in neonatal marmosets before examining the anatomic, physiological, and behavioral consequences. In adulthood, we observed perturbations in goal-orientated reach-and-grasp behavior, altered direction selectivity of V1 neurons, and changes in the cytoarchitecture throughout dorsal stream areas. This study highlights the importance of MT as a central node in visual system development and consequential visuomotor activity.

Mapping the neural circuitry of predator fear in the nonhuman primate.

In rodents, innate and learned fear of predators depends on the medial hypothalamic defensive system, a conserved brain network that lies downstream of the amygdala and promotes avoidance via projections to the periaqueductal gray. Whether this network is involved in primate fear remains unknown. To address this, we provoked flight responses to a predator (moving snake) in the marmoset monkey under laboratory conditions. We combined c-Fos immunolabeling and anterograde/retrograde tracing to map the functional connectivity of the ventromedial hypothalamus, a core node in the medial hypothalamic defensive system. Our findings demonstrate that the ventromedial hypothalamus is recruited by predator exposure in primates and that anatomical connectivity of the rodent and primate medial hypothalamic defensive system are highly conserved.