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Neurophysiological mechanisms of tool use by monkeys and humans

This project, being carried out in collaboration with Atsushi Iriki (RIKEN Brain Sciences Institute, Tokyo), is probing single cell activity in the motor (M1) and premotor cortex (PMv, PMd) during tool use by monkeys. These areas are of critical importance for the visual guidance of grasp, for example shaping the hand to grip a pen or using a tool. Populations of neurons in these cortical areas are recorded during performance of a task that involves use of a simple tool, a rake, to collect food rewards. We know that a special component of the corticospinal tract, the cortico-motoneuronal (CM) system is well-developed in primate species that can perform skilled hand movements and, in particular, use tools. The project is seeking evidence that CM neurons are active during tool use, an issue of fundamental importance in understanding the development of brain motor mechanisms that underpinned the evolution of tool use by primates.

We recently used non-invasive MRI and voxel-based morphometry (VBM) to detect changes in brain structure in three adult Japanese macaques trained to use a rake to retrieve food rewards. Monkeys, who were naive to any previous tool use, were scanned repeatedly over 6 weeks, comprising 2 weeks of habituation followed by 2 weeks of intensive daily training and a 2-week post-training period. VBM analysis revealed significant increases in gray matter in with rake performance across the three monkeys. The effects were most significant in the right superior temporal sulcus, right second somatosensory area, and right intraparietal sulcus, with less significant effects in these same regions of the left hemisphere.

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A further planned project involves working with human volunteers to gain a better understanding of the pattern of muscle activity that underlies tool use of this kind. In collaboration with ION Functional Imaging Laboratory, magnetoencephalographic (MEG) recordings will be used during tool use by volunteers.

Reference

Quallo MM, Price CJ, Ueno K, Asamizuya T, Cheng K, Lemon RN, Iriki A (2009) Gray and white matter changes associated with tool-use learning in macaque monkeys. Proc Natl Acad Sci USA 106:18379-18384.