It has been suggested that inhibitory executive control of behavior is directed by the frontal lobes. We used functional magnetic resonance imaging to explore the brain regions that are involved in the inhibition of habitual manual responses. Fifteen right-handed subjects performed the rock–scissors– paper game against computer-simulated pictures of hands during the scanning procedure. The subjects were required to win, lose, or draw against the presented picture in a separate block. We considered that the situation in which subjects intentionally lost the game required the suppression of habitual behavior, because it is natural behavior for people to attempt to win the game. Compared with the WIN and DRAW conditions, the left premotor and sensorimotor areas were activated for both hand sessions with a positive correlation with error rates. Importantly, the LOSE condition in the case of the right hand yielded brain activation exclusively in the anterior part of the left inferior frontal gyrus, the activity which showed a negative correlation with error rates. Overall brain activations were predominant in the left hemisphere, irrespective of the hand used for the response. The results suggest that the anterior part of the left inferior frontal gyrus plays a critical role in the inhibition of habitual manual behavior, and that the left hemisphere is dominant for the selection of well-learned manual behavior.

The neural activities for color word interference effects were investigated using event-related brain potentials (ERPs) recorded in a flanker-type interference task. Kanji words (Japanese morphograms) and kana words (Japanese phono-grams) were used as the flanker stimuli to obtain insights about hemispheric specialization for processing two types of Japanese orthographies. Interference effects in reaction time were larger when kanji words were presented in the left visual field and when kana words were in the right visual field. ERPs were modulated by the incongruent flankers, which generated a negative ERP component with the different onset and offset depending on flanker attributes. Consistent with the behavioral data, the interference-related negativity was observed for kanji words presented in the left visual field and for kana words in the right visual field. The negativity distributed maximally over the fronto-central site. The early part of the negativity distributed strongly over the frontal midline area, whereas it extended bilaterally over the frontal area in the late phase. The present results support the view of preferential processing of kanji in the right hemisphere and that of kana in the left hemisphere. The temporal profile of scalp topographies for the interference-related neural activity suggests that the medial and dorsolateral prefrontal regions may be involved in maintaining attentional set and conflict resolution.

The cerebellum has been implicated in higher cognitive functions including learning, memory, and attention as well as its well-known role in motor programming. Recent studies have suggested that the cerebellum plays a role in shifts of attention. We investigated the contribution of the cerebellum to visuospatial attentional ability in a trial-by-trial cueing task involving the covert orienting of spatial attention. We recorded event-related evoked potentials (ERPs) and reaction times (RTs) in patients with cerebellar degenerative disorders affecting mainly the lateral cerebellum and compared them to age-matched controls. The RT data demonstrated that both the cerebellar patients and control subjects responded to the valid cues faster than to the invalid cues for both the central and the peripheral cues. Consistent with the RT data, the ERP data showed a comparable generation of attention shift-related negativities during the cue-target interval for both the central and the peripheral cue experiments. The early negative component of the ERP to the target was also comparably modulated in both groups as a function of cue validity, suggesting efficient facilitation of sensory pathways by prior allocation of spatial attention to the cued place. Conversely, the late negative deflection preceding the imperative target stimulus and the late sustained positivity following target presentation, which reflect neural activities for response preparation and selection, were reduced in the cerebellar group. These findings suggest that the lateral cerebellum makes little contribution to visuospatial attention shift in either the voluntary or automatic modes and support a role of the lateral cerebellum in the neural system required for response preparation and selection.