Multimodal output mapping of human central motor representation on different spatial scales

Abstract

Non‐invasive mapping by focal transcranial magnetic stimulation (TMS) is frequently used to investigate cortical motor function in the intact and injured human brain. We examined how TMS‐derived maps relate to the underlying cortical anatomy and to cortical maps generated by functional imaging studies. The centres of gravity (COGs) of TMS maps of the first dorsal intersosseus muscle (FDI) were integrated into 3‐D magnetic resonance imaging (MRI) data sets in eleven subjects. In seven of these subjects the TMS‐derived COGs were compared with the COG of regional cerebral blood flow increases using positron emission tomography (PET) in an index finger flexion protocol. Mean TMS‐derived COG projections were located on the posterior lip of the precentral gyrus and TMS‐derived COG projections were in close proximity to the mean PET‐derived COG, suggesting that the two methods reflect activity of similar cortical elements. Criteria for a reliable assessment of the COG and the number of positions with a minimum amplitude of two‐thirds of the maximum motor‐evoked potential (T3Ps) were determined as a function of the number of stimuli and extension of the stimulation field. COGs and T3Ps were compared with an estimate of the size of the human motor cortex targeting α‐motoneurons of forearm muscles. This comparison suggests that TMS can retrieve spatial information on cortical organization below the macroanatomic scale of cortical regions. Finally, we studied the cortical representation of hand muscles in relation to facial and foot muscle representations and investigated hemispherical asymmetries. We did not find any evidence for a different ipsi‐ or contralateral representation of the mentalis muscle. Also, no difference was found between FDI representations on the dominant versus the non‐dominant hemisphere.

Role of the Primary Motor and Dorsal Premotor Cortices in the Anticipation of Forces during Object Lifting

“…Projected coil trajectories for the primary motor cortex showed greater variability. This is likely because we made adjustments in coil positioning to target where stimulation resulted in the maximum MEP amplitude; previous studies have reported that this location can vary among individuals (Classen et al, 1998).…”

Congenitally altered motor experience alters somatotopic organization of human primary motor cortex

“…110% MT intensity was then used to map both muscles' representations. Maps were derived by acquiring 5 MEPs of the target muscle with the stimulator at 110% of MT at locations on the 1 ϫ 1 cm grid constructed around CZ (24). Mapping proceeded in an anterior-posterior and medial-lateral direction until at least 4/5 MEPs were absent.…”

“…For the targeted muscle, there is usually one small circumscribed area from which the largest MEP responses can be elicited (referred to as a ''hot spot'') with smaller responses being evoked from adjacent positions (24). In accordance with the medial and lateral M1 activation demonstrated by fMRI, the motor maps of the target foot muscle in Füsslers S2 and S3 were not only extensive but also showed two distinct areas, or hot spots, from which maximal MEP responses were elicited-one medial and one lateral ( Fig.…”

“…To map the locations from which TMS elicits MEPs in the target muscle, a 1 ϫ 1 cm grid with the intersection of the interaural and the nasion-inion lines (CZ) at its origin was marked on the subject's scalp (24). For the targeted muscle, there is usually one small circumscribed area from which the largest MEP responses can be elicited (referred to as a ''hot spot'') with smaller responses being evoked from adjacent positions (24).…”

Task-oriented treadmill exercise training in chronic hemiparetic stroke

“…The TM training model leverages three physiological principles: (1) improved reflexive gait patterning attributed to altered afferent proprioceptive input, (2) augmented locomotor entrainment with task-repetition that animal and human studies show is crucial for motor learning [39][40], and (3) progression of metabolic demands of the training stimulus by increasing velocity, grade, training session duration, and total program length. The latter principle of progression raises fundamental questions regarding which exercise formulas can optimally improve functional and metabolic health outcomes.…”