CEREBRAL ORGANIZATION OF MOTOR IMAGERY : Contralateral Control of Grip Selection in Mentally Represented Prehension

219 Abstract— The principle of contralateral organization of the visual and motor systems was exploited to investigate contributions of the cerebral hemispheres to the mental representation of prehension in healthy, right-handed human subjects. Graphically rendered dowels were presented to either the left or right visual field in a variety of different orientations, and times to determine whether an underhand or overhand grip would be preferred for engaging these stimuli were measured. Although no actual reaching movements were performed, a significant advantage in grip-selection time was found when information was presented to the cerebral hemisphere contralateral to the designated response hand. Results are consistent with the position that motor imagery recruits neurocognitive mechanisms involved in movement planning. More precisely, these findings indicate that processes within each cerebral hemisphere participate in mentally representing object-oriented actions of the contralateral hand. An important contribution to resolving the long-standing debate over the relationship between imagery and perception has been made by numerous studies indicating that the two categories of behavior involve common neural substrates (for comprehensive reviews, see Farah, 1988; Kosslyn, 1994). Disorders of visual perception following brain injury are often accompanied by corresponding changes in imagery abilities (e. processing areas during the performance of like-modality imagery tasks. As a result of this evidence, the so-called imagery debate is no longer focused on whether imagery and perception involve common structures, but instead on articulating the details of this relationship. For instance, recent observations of intact imagery in an associative agnosic patient have led to the proposal that visual imagery and perception may involve separate routes of access to a common system of representations (Behrmann, Winocur, & Mosco-vitch, 1992). In addition, although some functional neuroimaging studies of imagery have found patterns of activation that include the primary visual cortex (e.g., Kosslyn et al., 1993), others have failed to detect such involvement (e.g., Roland & Gulyas, 1994a, 1994b). In short, evidence from cognitive neuroscience suggests that imagery and perception involve many, but perhaps not all, of the same neurocogni-tive mechanisms. The involvement of common mechanisms in imagery and behavior appears not to be restricted to the perceptual domain. Despite having received considerably less attention, a growing body of evidence suggests that motor imagery and action also involve common neural sub-strates (for a comprehensive review, see Jeannerod, 1994). For example, studies of patients with Parkinson's disease (e. indicate that impairments in motor behavior are often accompanied by comparable …