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The neglected medial part of macaque area PE: segregated processing of reach depth and direction
Marina De Vitis1,2,3, Rossella Breveglieri1, Konstantinos Hadjidimitrakis1,4,5
1Department of Biomedical and Neuromotor Sciences, University of Bologna, Piazza di Porta S. Donato 2, 40126, Bologna, Italy.
Abstract:
Area PE (Brodmann's area 5), located in the posterior parietal cortex (PPC), is involved in the control of arm movements. Many monkey studies showed PE's involvement in reach directions, while only a few revealed signals coding the depth of reaches. Notably, all these studies focused on the lateral part of PE, leaving its medial part functionally largely unexplored. We here recorded neuronal activity in the medial part of PE in three male Macaca fascicularis while they performed coordinated eye and arm movements in darkness towards targets located at different directions and depths. We used the same task as in our previous studies of more caudal PPC sectors (areas V6A and PEc), allowing a direct comparison between these three PPC areas. We found that, in medial PE, reach direction and depth were encoded mainly by distinct populations of neurons. Directional signals were more prominent before movement onset, whereas depth processing occurred mainly during and after movement execution. Visual and somatosensory mapping of medial PE revealed a lack of visual responses yet strong somatosensory sensitivity, with a representation of both upper and lower limbs, distinct from the somatotopy reported in lateral PE. This study shows that PE is strongly involved in motor processing of depth and direction information during reaching. It highlights a trend in medial PPC, going from the joint coding of depth and direction signals caudally, in area V6A, to a largely segregated processing of the two signals rostrally, in area PE.
Insights
Researchers explored the medial part of Brodmann's area 5 (PE) in the posterior parietal cortex, finding distinct neuronal populations for reach direction and depth. This area shows strong somatosensory responses, contributing to motor control.
Area of Science:
- Neuroscience
- Motor Control
- Parietal Cortex Function
Background:
- The posterior parietal cortex (PPC), specifically Brodmann's area 5 (PE), is implicated in arm movement control.
- Previous research primarily investigated the lateral part of PE, leaving the medial region functionally underexplored.
- Existing studies show PE's role in reach direction, with limited data on depth processing.
Purpose of the Study:
- To investigate neuronal activity in the medial part of area PE during coordinated eye and arm movements.
- To compare the functional role of medial PE with caudal PPC areas (V6A and PEc) in processing reach direction and depth.
- To characterize the sensory responses and somatotopy of medial PE.
Main Methods:
- Neuronal recordings were performed in the medial PE of three male Macaca fascicularis.
- Subjects executed a task involving coordinated eye and arm movements towards targets at various directions and depths in darkness.
- Visual and somatosensory mapping of medial PE was conducted.
Main Results:
- Medial PE neurons primarily encoded reach direction and depth using distinct populations.
- Directional signals were more prominent pre-movement, while depth processing occurred during and post-movement.
- Medial PE showed minimal visual responses but strong somatosensory sensitivity, representing upper and lower limbs differently than lateral PE.
Conclusions:
- Medial area PE plays a significant role in the motor processing of reach depth and direction.
- A rostral to caudal trend in the medial PPC shows a shift from joint coding (V6A) to segregated processing (PE) of depth and direction.
- Medial PE contributes uniquely to sensorimotor integration for reaching movements.
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