Cortical connections of the functional domain for climbing or running in posterior parietal cortex of galagos

Reversible deactivation of motor cortex reveals that areas in parietal cortex are differentially dependent on motor cortex for the generation of movement

Primates are characterized by specializations for manual manipulation, including expansion of posterior parietal cortex (PPC) and, in Catarrhines, evolution of a dexterous hand and opposable thumb. Previous studies examined functional interactions between motor cortex and PPC in New World monkeys and galagos, by inactivating M1 and evoking movements from PPC. These studies found that portions of PPC depend on M1 to generate movements. We now add a species that more closely resembles humans in hand morphology and PPC: macaques. Inactivating portions of M1 resulted in all evoked movements being reduced (28%) or completely abolished (72%) at the PPC sites tested (in areas 5L, PF, and PFG). Anterior parietal area 2 was similarly affected (26% reduced and 74% abolished) and area 1 was the least affected (12% no effect, 54% reduced, and 34% abolished). Unlike previous studies in New World monkeys and galagos, interactions between both nonanalogous (heterotopic) and analogous (homotopic) M1 and parietal movement domains were commonly found in most areas. These experiments demonstrate that there may be two parallel networks involved in motor control: a posterior parietal network dependent on M1 and a network that includes area 1 that is relatively independent of M1. Furthermore, it appears that the relative size and number of cortical fields in parietal cortex in different species correlates with homotopic and heterotopic effect prevalence. These functional differences in macaques could contribute to more numerous and varied muscle synergies across major muscle groups, supporting the expansion of the primate manual behavioral repertoire observed in Old World monkeys.NEW & NOTEWORTHY Motor cortex and anterior and posterior parietal cortex form a sensorimotor integration network. We tested the extent to which parietal areas could initiate movements independent of M1. Our findings support the contention that, although areas 2, 5L, PF, and PFG are highly dependent on M1 to produce movement, area 1 may constitute a parallel corticospinal pathway that can function somewhat independently of M1. A similar functional architecture may underlie dexterous tool use in humans.

Thalamic connections of the caudal part of the posterior parietal cortex differ from the rostral part in galagos (Otolemur garnettii)

In this study, thalamic connections of the caudal part of the posterior parietal cortex (PPCc) are described and compared to connections of the rostral part of PPC (PPCr) in strepsirrhine galagos. PPC of galagos is divided into two parts, PPCr and PPCc, based on the responsiveness to electrical stimulation. Stimulation of PPC with long trains of electrical pulses evokes different types of ethologically relevant movements from different subregions ("domains") of PPCr, while it fails to evoke any movements from PPCc. Anatomical tracers were placed in both dorsal and ventral divisions of PPCc to reveal thalamic origins and targets of PPCc connections. We found major thalamic connections of PPCc with the lateral posterior and lateral pulvinar nuclei, distinct from those of PPCr that were mainly with the ventral lateral, anterior pulvinar, and posterior nuclei. The anterior, medial, and inferior pulvinar, ventral anterior, ventral lateral, and intralaminar nuclei had fewer connections with PPCc. Dominant connections of PPCc with lateral posterior and lateral pulvinar nuclei provide evidence that unlike the sensorimotor-orientated PPCr, PPCc is more involved in visual-related functions.

Thalamocortical and corticothalamic connections of multiple functional domains in posterior parietal cortex of galagos

In prosimian galagos, the posterior parietal cortex (PPC) is subdivided into a number of functional domains where long-train intracortical microstimulation evoked different types of complex movements. Here, we placed anatomical tracers in multiple locations of PPC to reveal the origins and targets of thalamic connections of four PPC domains for different types of hindlimb, forelimb, or face movements. Thalamic connections of all four domains included nuclei of the motor thalamus, ventral anterior and ventral lateral nuclei, as well as parts of the sensory thalamus, the anterior pulvinar, posterior and ventral posterior superior nuclei, consistent with the sensorimotor functions of PPC domains. PPC domains also projected to the thalamic reticular nucleus in a somatotopic pattern. Quantitative differences in the distributions of labeled neurons in thalamic nuclei suggested that connectional patterns of these domains differed from each other.