This study, as originally proposed, uses single neuron recording techniques in behaving primates with the aim of deciphering the movement parameters encoded and the nature of the information represented in the cerebellum. The cerebellar cortex and nuclei play a major role in the production of smooth, coordinated movements. There are a host of hypotheses on the cerebellum's role in motor behavior. Testing the validity of any hypothesis of cerebellar function will require defining the parameters that modulate the functional """"""""activity"""""""" in the cerebellum and understanding how these parameters are encoded or represented in the discharge of cerebellar neurons. These are crucial steps in understanding the variables controlled and the information processed by the cerebellum. This conceptual approach forms the basis for this work initially proposed only at the level of neuron recording in behaving monkeys but extended to synergistic studies in humans with the recent exciting developments in functional magnetic resonance imaging. In the last funding year, our aim has been to define in the whole brain areas in the cerebral and cerebellar cortex and subcortical nuclei engaged in the execution of a complex, visually guided movement task. Accurate, visually guided movements require a complex series of integrative steps that transform retinal information into an appropriate motor output. Two major pathways have been implicated in the function of the primate visual system during spatial control of motor movement, the dorsal and the ventral stream, respectively. The dorsal stream connects the striate and extrastriate cortices to areas around the intraparietal sulcus and posterior parietal region. The posterior parietal region connects reciprocally to the motor, premotor and prefrontal cortices. Furthermore, there is evidence of thalamic involvement (e.g. pulvinar) as an important relay station as well as participation of cortico-ponto-cerebellar pathways. The dorsal stream is thought to be involved in the transformation of visual information into motor commands, whereas the ventral stream, projecting from the occipital cortex to the inferotemporal lobe, is proposed to be involved in off-line object recognition.
The aim of the present experiments is to examine the hypothesis that in humans, the cortical stream of activation and their subcortical and cortico-cerebellar modulations will correspond to the presumed visuomotor pathways mapped in primates. The paradigm employed for these studies requires subjects to use a joystick to move a hair cross cursor on a rear projection screen. Two sets of eight targets are arranged in circle (45o intervals) around a center start box and appear at two different distances in the same direction. During the task periods, the participants must use the joystick to move the cross-hair from the center start box first to the shorter distance target and then to the target at the greater distance. During the rest periods the volunteers lie motionless looking at a colored box on a lighted screen. Various other tasks are also planned to control for just oculomotor activity, or motor function without visual guidance, etc. Data evaluation relies on first generating individual maps, and then warping each individual map to Talairach coordinates. Subsequently, a composite activation map is generated by superimposing all individual maps and displaying a pixel as """"""""activated"""""""" if and only if it was considered """"""""activated"""""""" in at least 75% the individual maps. Based on these composite maps a final map is created displaying the results of the comparison between tasks. In a set of completed studies that will be presented as an abstract in the ISMRM meeting in April 1997, we observed a pattern of activation during the visually guided movement that is consistent with the flow of information from striate and extrastriate areas, to the superior and inferior parietal lobe and to frontal motor areas, similar to that of the dorsal stream described in primates.
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