Part Of Dorsal Premotor Cortex Research Articles

Does Transcranial Magnetic Stimulation (TMS) primarily target premotor or motor cortex in precentral gyrus?

TMS can be used to map the corticomotor representations of hand muscles (HMs) in the precentral gyrus (PG), whose spatial peak is often not located in the primary motor hand area (M1HAND) but shifts towards the caudal part of dorsal premotor cortex (PMd). We used magnetic resonance imaging (MRI) to test the hypothesis that “hand-knob” of PG shows different structural properties in individuals with a “premotor” representation compared to individuals with a “primary-motor” representation of HMs. Twenty-four volunteers underwent MRI and sulcus-shape-based TMS-mapping of right PG. T1-weighted-MRIs were used for neuronavigation and to calculate cortical-thickness of the PG. We also performed quantitative multiparameter mapping of the longitudinal relaxation rate as an index of cortical myelination and simulated the electric field strength induced by TMS in the hand-knob-region. In 14 out-of 24 individuals (58%), TMS mapping disclosed a spatial peak in the PMd (“PMd-subjects”), whereas the remaining 10 subjects (42%) showed maximal motor response in M1HAND (“M1HAND-subjects”). “M1-subjects” displayed a higher electric field strength in the rostral part of the M1HAND (p = 0.01). “PMd-subjects” showed an increase of regional-myelination in the PG (p = 0.033). The results support the notion of two distinct functional-microstructural phenotypes of corticomotor hand representations in human PG.

T122. Does TMS primarily target premotor or motor cortex in precentral gyrus?

Introduction Transcranial magnetic stimulation (TMS) can be used to map the corticomotor representations of hand muscles in the precentral gyrus. The spatial peak of the corticomotor representations is often not located in the primary motor hand area (M1HAND), but shows an anterior shift towards the caudal part of dorsal premotor cortex (PMd). Here we used magnetic resonance imaging (MRI) to test the hypothesis that the “hand knob” of the precentral gyrus shows different structural properties in individuals with a clear “premotor” representation compared to individuals with a preponderant “primary-motor” representation of hand muscles. Methods Twenty-four volunteers (mean age: 24.3 ± 0.9 SE, 12 women) underwent whole-brain structural MRI and sulcus-shape based TMS mapping of the right precentral gyrus. High-resolution T1-weighted MRIs were used for neuronavigation of TMS and to calculate regional cortical thickness of the precentral gyrus. We also performed quantitative multiparameter mapping of the longitudinal relaxation rate (R1 = 1/T1) as an index of cortical myelination and simulated the electric field strength induced by TMS at motor threshold (—E—) in the hand-knob region (SimNIBS software). Sulcus-shape based TMS mapping was used to obtain mediolateral and posterior-anterior corticomotor excitability profiles of the left abductor digiti minimi and first dorsal interosseus muscles. Results In 14 out of 24 individuals (58%), TMS mapping disclosed a clear spatial peak in the PMd (referred to as “PMd” subjects”), whereas the remaining 10 subjects (42%) showed maximal motor responses more posteriorly in M1HAND (referred to as M1HAND subjects). Motor threshold was not different between the two groups (p = 0.265). Compared “PMd” subjects, “M1” subjects displayed a higher electric field strength in the very rostral part of the M1HAND in the transition zone from the wall to the crown of the precentral gyrus (p = 0.01). In addition, “PMd” subjects showed an overall increase of regional myelination in the precentral gyrus relative to the “M1” subjects (mixed model ANOVA: F(1,18) = 5.362, p = 0.033). No difference between two groups was evident for curvature and cortical thickness. Conclusion Differences in location of the “motor hot spot” are associated with differences in microstructure in the precentral gyrus and the magnitude of the induced electrical field. The results support the notion of two distinct functional and microstructural phenotypes of corticomotor hand representations in human precentral gyrus. They also underscore the usefulness of electrical field modelling to account for inter-individual differences in the biophysiological effects of TMS in the human brain.

Distribution of Activity Across the Monkey Cerebral Cortical Surface, Thalamus and Midbrain during Rapid, Visually Guided Saccades

To examine the distribution of visual and oculomotor activity across the macaque brain, we performed functional magnetic resonance imaging (fMRI) on awake, behaving monkeys trained to perform visually guided saccades. Two subjects alternated between periods of making saccades and central fixations while blood oxygen level dependent (BOLD) images were collected [3 T, (1.5 mm)3 spatial resolution]. BOLD activations from each of four cerebral hemispheres were projected onto the subjects' cortical surfaces and aligned to a surface-based atlas for comparison across hemispheres and subjects. This surface-based analysis revealed patterns of visuo-oculomotor activity across much of the cerebral cortex, including activations in the posterior parietal cortex, superior temporal cortex and frontal lobe. For each cortical domain, we show the anatomical position and extent of visuo-oculomotor activity, including evidence that the dorsolateral frontal activation, which includes the frontal eye field (on the anterior bank of the arcuate sulcus), extends anteriorly into posterior principal sulcus (area 46) and posteriorly into part of dorsal premotor cortex (area 6). Our results also suggest that subcortical BOLD activity in the pulvinar thalamus may be lateralized during voluntary eye movements. These findings provide new neuroanatomical information as to the complex neural substrates that underlie even simple goal-directed behaviors.

Location of the polysensory zone in the precentral gyrus of anesthetized monkeys.

Neurons in the premotor cortex of macaques respond to tactile, visual and auditory stimuli. The distribution of these responses was studied in five anesthetized monkeys. In each monkey, multiunit activity was studied at a grid of locations across the precentral gyrus. A cluster of sites with polysensory responses was found posterior to the genu of the arcuate sulcus. Tactile and visual responses were represented in all five monkeys, while auditory responses were rarer and found in only two monkeys. This polysensory zone (PZ) was located in the caudal part of premotor cortex. It varied in extent among the monkeys. It was mainly ventral to the genu of the arcuate, in the dorsal and caudal part of the ventral premotor cortex (PMv). In some monkeys it extended more dorsally, into the caudal part of dorsal premotor cortex (PMd). Sensory responses were almost never found in the rostral part of PMd. We suggest that the polysensory zone may contribute to the guidance of movement on the basis of tactile, visual and auditory signals.