Lesions in Posterior Parietal Area 5 in Monkeys Result in Rapid Behavioral and Cortical Plasticity

Abstract

We examined the effects of focal lesions of posterior parietal area 5 in macaque monkeys on bimanual behavior performed with and without visual guidance. The animals were trained on two reaching tasks and one tactile texture discrimination task. Task 1 simply involved reaching toward and grasping a reward from one of five well positions. Task 2 required the monkey to use both hands simultaneously to obtain a reward. The tactile texture discrimination task required the monkey to signal the roughness of a passively delivered texture using its jaw. Following lesions to area 5, the monkeys showed a decrease in hand use for tasks 1 and 2 and an inability to perform task 2 in specific locations in visual space. These deficits recovered within several days. No deficits were observed in the tactile texture discrimination task, or in an analgesic control monkey. Electrophysiological recordings made just prior to the lesion, immediately following the lesion, and 2 months following the lesion demonstrated that cortical areas just rostral to the lesioned area 5, areas 1 and 2, were topographically reorganized and that receptive fields for neurons in these fields changed location on the body surface. These cortical map changes are correlative and may, in part, contribute to the rapid behavioral recovery observed. The mechanism for such rapid changes may be the unmasking of existing divergent and convergent thalamocortical connections that are part of the normal cortical circuitry.

Posterior parietal cortex contains a command apparatus for hand movements

“…The deficit in tactile apraxia appears to represent an isolated disturbance of the fine dexterous hand movements that are required to interact with an object. A similar, although less dramatic, deficit has been observed in the monkey following lesions to lateral area 5 (32). Tactile apraxia in humans is generally accompanied by an impairment of tactile gnosis (astereognosis).…”

Synchronization patterns suggest different functional organization in parietal reach region and dorsal premotor cortex

“…PRR lesions (Padberg et al 2010;Rushworth et al 1997aRushworth et al , 1997b and inactivation (Hwang et al 2012;Yttri et al 2014) have repeatedly shown that reach trajectories and end points are severely affected by a compromised parietal cortex, although the ability to select between two different types of movement ("push" vs. "pull") that were instructed by different cognitive rules (colors) remained unaffected (Rushworth et al 1997a). Human patients with parietal lesions have long been known to suffer from optic ataxia and the inability to reach precisely to specific targets, part of Balint's syndrome (for review see Andersen et al 2014).…”

“…By comparison, in PMd the amplitude of neural responses during anti reaches tends to be 15% higher than during pro reaches, indicating the preference of PMd neural populations for indirect rule-based motor goal construction (Gail et al 2009). Finally, PRR lesions affect the ability to reach to specific spatial locations but not the rule-based selection between motor goals (Hwang et al 2012;Padberg et al 2010;Rushworth et al 1997aRushworth et al , 1997bYttri et al 2014), while PMd lesions impair the acquisition of new arbitrary stimulus-response associations (Passingham 1986;Petrides 1982).…”

Fabrication of an inexpensive, implantable cooling device for reversible brain deactivation in animals ranging from rodents to primates

“…Unfortunately, removal of cortical tissue permanently alters the region of interest and ultimately not only affects the area ablated but also can lead to retrograde degeneration of connected cortical areas and subcortical nuclei, leading to permanent changes in the entire network. While interesting in and of itself, such plasticity can confound the study of the ablated region's normal function (e.g., Padberg et al 2010). For this reason, reversible deactivation through cooling or injection of chemicals is valuable for providing important insights into how normal circuits function in real time.…”