We investigated the neurological basis for efficacy of prism adaptation therapy, which is used for the treatment of poststroke unilateral spatial neglect (USN). Study subjects were 6 USN-positive (+), 6 USN-negative patients, and 6 healthy volunteer control subjects. USN was identified by the Behavioural Inattention Test (BIT). During the tasks, brain activity was assessed with fNIRS via changes in oxyHb concentration per unit length. There was no significant difference in the number of errors in the task between the 3 groups. However, in the USN(+) group there was a significantly greater reduction in oxyHb levels in the right parietal association cortex during the prism adaptation task than in the other 2 groups ( ). There was an immediate improvement in USN symptoms as well as a significant increase in oxyHb levels during the prism adaptation in the channels covering the right frontal and parietal lobes in 2 patients in the USN(+) group ( ). This result suggested that decreased activity in the right parietal association cortex, which is related to spatial perception, during the prism adaptation task and task-induced reorganization of the right frontal and parietal areas were involved in improvement in USN symptoms. 1. Introduction Recently, it was shown that prism adaptation therapy not only instantly improved unilateral spatial neglect (USN) symptoms but also enhanced balancing ability in patients with USN after stroke [1, 2]. Also reported has been the use of prism adaptation therapy for the treatment of USN to achieve improvement in USN symptoms as well as in movements [1–3]. This therapy is aimed at inducing the USN patient to pay attention to the neglect space by reaching out with an upper limb toward an object using deviated visual information caused by a prism [1]. The prism deviates the visual information so soon after the start of the task that the patient cannot precisely reach an object. However, repeated attempts enable the patient to successfully reach the object through adaptive learning [4]. When the patient attempts such reaching movements under normal visual conditions without prism-mounted eyeglasses after prism adaptation therapy, the patient’s motion deviates to the opposite side of the object as an aftereffect. Hence, the prism adaptation task has a physical exercise component as well as an adaptive process of feedback control of deviated movements so that the brain is forced to correct or reorganize spatial perception. Neural mechanisms of action for these prism adaptation effects have been reported exclusively in healthy
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