Contribution of the primary motor cortex to motor imagery: A subthreshold TMS study

• Published in: Human brain mapping Vol. 32; no. 9; pp. 1471 - 1482
• Main Authors: Pelgrims, Barbara, Michaux, Nicolas, Olivier, Etienne, Andres, Michael
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-09-2011; Wiley-Liss; John Wiley & Sons, Inc
• Subjects: Adult; Analysis of Variance; Biological and medical sciences; Brain mapping; Brodmann's area; Cerebrospinal fluid. Spinal cord. Spinal roots. Spinal nerves; Cortex (motor); Electroencephalography - methods; Electromyography; EMG; Evoked Potentials, Motor - physiology; Functional Laterality - physiology; Hand; Hand - innervation; Humans; Imagination - physiology; Information processing; Investigative techniques, diagnostic techniques (general aspects); Judgment; laterality; Male; Medical sciences; mental rotation; mental task performance; Motor Cortex - physiology; motor representations; Motor task performance; Movement - physiology; Muscles; Nervous system; Neurosurgery; Orientation; Photic Stimulation - methods; proprioception; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Reaction Time - physiology; Reaction time task; rTMS; Semantics; Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases; Time Factors; Transcranial Magnetic Stimulation; Mental rotation; Nervous system diseases; Motor pathway; Radiodiagnosis; Proprioception; Central nervous system; Representation; Imagery; Encephalon; Motor cortex; motor representations; Laterality; rTMS
• ISSN: 1065-9471; 1097-0193; 1097-0193
• DOI: 10.1002/hbm.21121

Motor imagery (MI) mostly activates the same brain regions as movement execution (ME) including the primary motor cortex (Brodmann area 4, BA4). However, whether BA4 is functionally relevant for MI remains controversial. The finding that MI tasks are impaired by BA4 virtual lesions induced by transcranial magnetic stimulation (TMS) supports this view, though previous studies do not permit to exclude that BA4 is also involved in other processes such as hand recognition. Additionally, previous works largely underestimated the possible negative consequences of TMS‐induced muscle twitches on MI task performance. Here we investigated the role of BA4 in MI by interfering with the function of the left or right BA4 in healthy subjects performing a MI task in which they had to make laterality judgements on rotated hand drawings. We used a subthreshold repetitive TMS protocol and monitored electromyographic activity to exclude undesirable effects of hand muscle twitches. We found that BA4 virtual lesions selectively increased reaction times in laterality judgments on hand drawings, leaving unaffected a task of equal difficulty, involving judgments on letters. Interestingly, the effects of virtual lesions of left and right BA4 on MI task performance were the same irrespective of the laterality (left/right) of hand drawings. A second experiment allowed us to rule out the possibility that BA4 lesions affect visual or semantic processing of hand drawings. Altogether, these results indicate that BA4 contribution to MI tasks is specifically related to the mental simulation process and further emphasize the functional coupling between ME and MI. Hum Brain Mapp , 2010. © 2010 Wiley‐Liss, Inc.