title: Effect of the number of response alternatives on brain activity in response selection.
abstract: It is well-known in motor control literature that a response time (RT) increases as a logarithmic function of the number of response alternatives (NA) (Hick's law). In this study, we identified neural correlates for this relationship using event-related functional MRI and a choice finger-movement task. Behaviorally, average RTs of all subjects increased as a logarithmic function of the NA in accordance with the law. From a voxel-wise search for brain areas where the activity was correlated with NA and thence the RT, a positive correlation was found at the posterior cingulate and left superior frontal gyri, whereas a negative correlation was observed at areas in bilateral inferior parietal lobules. This differential modulation by the task context, namely, the NA available for a choice response with identical stimulus and response, indicates that these regions are involved in various aspects of response selection, intentional retrieval of motor program, or spatial expectancy.
authors.affiliation: Interdisciplinary program of Cognitive Sciences, College of Medicine, Seoul National University, Chongno-Gu, Seoul, Korea.
authors.forename: Sung-Ho
authors.initials: SH
authors.lastname: Woo
authors.forename: Kyoung-Min
authors.initials: KM
authors.lastname: Lee
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000502:physiology*; D003071:Cognition / Q000502:physiology*; D003463:Cues; D003657:Decision Making / Q000502:physiology*; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006179:Gyrus Cinguli / Q000033:anatomy & histology / Q000502:physiology; D006801:Humans; D007257:Information Theory; D008279:Magnetic Resonance Imaging; D008297:Male; D009483:Neuropsychological Tests; D010296:Parietal Lobe / Q000033:anatomy & histology / Q000502:physiology; D010775:Photic Stimulation; D017397:Prefrontal Cortex / Q000033:anatomy & histology / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D013702:Temporal Lobe / Q000033:anatomy & histology / Q000502:physiology; D013997:Time Factors; D014793:Visual Cortex / Q000033:anatomy & histology / Q000502:physiology