The goal of this proposal is to improve our understanding of motor cortex organization. Motor cortex in mammals is organized in a rough somatotopic pattern, with the muscles of the hindlimb represented medially and the muscles of the forelimb and face represented progressively more laterally. Fine somatotopy is jumbled, however, and the reason for this is not clear. For example, within the forelimb representation, finger, hand, and arm are intermingled and appear multiple times. This contrasts with the fine somatotopy of primary somatosensory cortex. Recent studies in primates have suggested additional organizing principles that, together with large-scale somatotopy, may account more completely for motor topography. One alternative organizational feature in motor cortex is an apparent map of space to which the hand is driven by intracortical microstimulation (movement endpoint map). Regardless of initial hand position, stimulation of medial sites within the forelimb region drives the hand to locations near the feet, whereas stimulation at lateral sites drives the hand to locations near the head. A second alternative organizational feature is a patchwork of subregions, each representing a single complex, behaviorally relevant movement, such as feeding or flinching (ethological subregions map). I propose to test these alternatives in two non-primate species to determine whether either is a general organizing principle in mammals.
The specific aims are to: 1. Determine the organization and connections of motor and sensorimotor areas in the raccoon (Procyon lotor) using combined connectional, architectonic, microstimulation, and sensory mapping data. (This aim has been completed in squirrels). 2. Determine the movement topography and specific connections of motor cortex in California ground squirrels (Spermophilus beecheyi) and raccoons. The pattern of movement types evoked in the M1 forelimb representation by stimulation will be analyzed for similarities or organizations seen in monkey motor cortex. Connections to specific sites will be related to microstimulation results. These data from specific stimulation sites will be used to reinforce or refute functional interpretations of complex stimulation-evoked movements.
A basic understanding of brain organization is the first step toward developing new ways to diagnose and treat brain damage and disease. This proposal aims to improve the understanding to how the brain connects to and controls muscles.
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|Cooke, Dylan F; Padberg, Jeffrey; Zahner, Tony et al. (2012) The functional organization and cortical connections of motor cortex in squirrels. Cereb Cortex 22:1959-78|
|Krubitzer, Leah; Campi, Katharine L; Cooke, Dylan F (2011) All rodents are not the same: a modern synthesis of cortical organization. Brain Behav Evol 78:51-93|