Grant Number: 5R01NS031530-13
Project Title: Encoding of Reach-to-Grasp in the Primary Motor Cortex
PI Information: PROFESSOR TIMOTHY J. EBNER, ebner001@tc.umn.edu 

Abstract:
The global problem addressed by this proposal is how does the central nervous system (CNS) control a structure as complex as the primate hand? To begin to address this question, four Specific Aims are proposed that address three outstanding issues in the neural control of reach-to-grasp. The studies will use chronic single unit recordings in the primary motor cortex (M1) of monkeys trained to perform various reach-to-grasp movements. Extensive monitoring of arm and hand kinematics, grasp forces and the activity of arm and extrinsic/intrinsic muscles of the hand will be done. Statistical and analytical tools including regression analyses and data reduction techniques will be used to extract the neural representation of hand shape/object shape, kinematics, grasp forces and EMG activity. First, findings from psychophysical, lesion, and electrophysiological studies suggest that the CNS, at least in part, reduces the number of degrees of freedom by controlling the hand as a unit. Specific Aims 1 and 2 will address the hypothesis that neurons in the hand area of M1 encode and control hand shape/object properties, reflecting this global control of the hand. Second, early investigations into hand movements categorized prehension into two broad classes, power and precision grip and more elaborate classification systems followed. A prediction of these categorical schemes is that the CNS explicitly controls grasp type. More recent psychophysical studies, however, suggest that a strict division of hand posture into power and precision grasps does not occur. Specific Aim 3 will test the alternative hypothesis that power and precision are part of a continuum of hand postures in which hand shape is primarily controlled. A third major contemporary hypothesis is that reach and grasp are controlled by two independent but coupled channels: a "transport" channel that extracts information about the spatial location of objects to guide the reach and a "manipulation" channel that extracts information about the intrinsic properties of the object such as size and shape to guide hand shape. Although psychophysical results suggest that the two components are coupled, there is virtually no single unit data addressing this question. In Specific Aim 4 the hypothesis is tested that the reach and grasp components are coupled at the neuronal level in M1. In general understanding how the CNS controls prehension is a critical step in understanding human movements. In the future understanding the signals controlling grasp could prove useful for controlling prosthetic devices in patients with brain injury.

Thesaurus Terms:
arm, hand, limb movement, motor cortex, neural information processing, psychomotor function biomechanics, body physical characteristic, form /pattern perception, neuron, visual feedback, visual stimulus, wrist Macaca mulatta, behavior test, electromyography, histology, microelectrode, robotics, single cell analysis, stereotaxic technique

Institution: UNIVERSITY OF MINNESOTA TWIN CITIES
450 MCNAMARA ALUMNI CENTER, MINNEAPOLIS, MN 554552070
Fiscal Year: 2006
Department: NEUROSCIENCE
Project Start: 01-JAN-1994
Project End: 30-JUN-2008
ICD: NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE
IRG: IFCN

Purkinje Cells Signal Hand Shape and Grasp Force During Reach-to-Grasp in the Monkey

Carolyn R. Mason*, Claudia M. Hendrix* and Timothy J. Ebner

Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota

Submitted 11 May 2005; accepted in final form 6 September 2005

J Neurophysiol 95: 144-158, 2006. First published September 14, 2005

Two rhesus monkeys (1 female "G" at 5.2 kg, 1 male "L" at 6.8 kg) were trained to reach and grasp objects with an overhand grasp using specified force levels (Ojakangas and Ebner 1992 ). The animals sat in a primate chair with their heads fixed forward and facing a computer monitor (Fig. 1A). The animals initiated a trial by placing their hand on a start-pad located by their side. A "go" cue signaled the animals to reach ( 15 cm) and grasp the target object. The go cue also indicated the required grasp force level to be generated and maintained for that trial. As a result, the monkeys had a priori knowledge of the required force level before initiating the reach. Once the grasp was initiated, a red slider bar provided visual feedback of the grasp force being generated. If the monkeys successfully initiated and maintained the specified force level for 1.4 s, they received a juice reward. At the completion of 25 successful trials, the object was changed. The monkeys were not able to see their hands or the objects. However, before initiating the first trial of each block, the animals were allowed to identify the target object through touch. Therefore the animals were aware of the target object to be used before the initiation of a new block of trials.