title: Dissociable roles of preSMA in motor sequence chunking and hand switching-a TMS study.
abstract: Motor chunking, the grouping of individual movements into larger units, is crucial for sequential motor performance. The presupplementary motor area (preSMA) is involved in chunking and other related processes such as task switching, response selection, and response inhibition that are crucial for organizing sequential movements. However, previous studies have not systematically differentiated the role of preSMA in motor chunking and hand switching, thus leaving its relative contribution to each of these processes unclear. The aim of this study is to demonstrate the differential role of preSMA in motor chunking and hand switching. We designed motor sequences in which different kinds of hand switches (switching toward the right or left hand or continuing with the right hand) were counterbalanced across between- and within-chunk sequence points. Eighteen healthy, right-handed participants practiced four short subsequences (chunks) of key presses. In a subsequent task, these chunks had to be concatenated into one long sequence. We applied double-pulse transcranial magnetic stimulation (TMS) over left preSMA or left M1 areas at sequence initiation, between chunks, or within chunks. TMS over the left preSMA significantly slowed the next response when stimulation was given between chunks, but only if a hand switch toward the contralateral (right) hand was required. PreSMA stimulation within chunks did not interfere with responses. TMS over the left M1 area delayed responses with the contralateral hand, both within and between chunks. Both preSMA and M1 stimulation decreased response times at sequence initiation. These results suggest that left preSMA is not necessary for chunking per se, but rather for organizing complex movements that require chunking and hand switching simultaneously.
authors.affiliation: Human Motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland diana.muessgens@nih.gov.
authors.forename: Diana
authors.identifier: 0000-0001-6463-2232
authors.initials: D
authors.lastname: Muessgens
authors.affiliation: Human Motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland.
authors.forename: Nivethida
authors.initials: N
authors.lastname: Thirugnanasambandam
authors.affiliation: Human Motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Shitara
authors.affiliation: Human Motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland.
authors.forename: Traian
authors.initials: T
authors.lastname: Popa
authors.affiliation: Human Motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland.
authors.forename: Mark
authors.initials: M
authors.lastname: Hallett
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006225:Hand / Q000502:physiology*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000000981:diagnostic imaging / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D010775:Photic Stimulation; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: chunking; hand switching; motor sequence learning; presupplementary motor area; transcranial magnetic stimulation