Chapter 2. Prehension

74 THE PHASES OF PREHENSION
movements, with a pre-motion positivity above the precentral motor
cortex occurring at about 90 ms before detectable EMG activity in the
forearm. While this 80- 100 ms discharge in motor cortex prior to the
motor response has been firmly established, the contributions of other
regions is not as clear. In cortical and cerebellar studies in awake
performing primates, Lamarre and Chapman (1986) were able to
determine relative timing by recording neuronal activity from various
parietal and frontal areas and the cerebellum. They found parietal
regions initially respond to the stimulus about 180 ms prior to
movement, followed by responses in the lateral cerebellum 160-100
ms prior, and then motor cortical responses about 85 ms prior to
movement onset.
PLAN
thalamus c-) association -b mobr -b motor
limbic
cortex
lateral
cerebellum
u
move Ij
INTEND PROGRAM EVALUATE
Figure 4.5 Structures of the CNS involved in planning,
programming and execution of prehension movements (from
Paillard, 1982a; adapted by permission).
An intriguing model of how cortical and subcortical areas might be
involved in the planning and execution of movements was developed
by Allen and Tsukahara (1974) and extended by Paillard (1982a). As
seen in Figure 4.5, the regions of the cerebral cortex, basal ganglia
and cerebellum are all involved in the planning and program parame-
terization prior to movement initiation. Planning evolves within the
association cortex, the limbic cortex, lateral cerebellum and basal
ganglia, all of which send motor commands to the motor cortex. The
motor cortex, in turn, programs lower centers for the execution of the
movement (trajectory planning). Sensory information from the pe-