11 research outputs found
The effect of unpredicted visual feedback on activation in the secondary somatosensory cortex during movement execution
BACKGROUND: A mechanism that monitors the congruence between sensory inputs and motor outputs is necessary to control voluntary movement. The representation of limb position is constantly updated on the basis of somatosensory and visual information and efference copy from motor areas. However, the cortical mechanism underlying detection of limb position using somatosensory and visual information has not been elucidated. This study investigated the influence of visual feedback on information processing in somatosensory areas during movement execution using magnetoencephalography. We used an experimental condition in which the visual information was incongruent despite the motor execution and somatosensory feedback being congruent. Subjects performed self-paced bimanual movements of both thumbs, either symmetric or asymmetric, under normal visual and mirrored conditions. The mirror condition provided a visual feedback by showing a reflection of the subject’s right hand in place of the left hand. Therefore, in the Asymmetric task of the Mirror condition, subjects saw symmetric movements despite performing asymmetric movements. RESULTS: Activation in the primary somatosensory area (SI) revealed inhibition of neural activity and that in the secondary somatosensory area (SII) showed enhancement with voluntary movement. In addition, the SII contralateral to the side of stimulation was significantly enhanced in the Asymmetric task of the Mirror condition, which provided non-veridical visual feedback. CONCLUSIONS: These results suggested that visual information influenced the neuronal activity concerning sensorimotor interaction in the SII during motor execution. The SII contributes to the detection of unpredicted visual feedback of movement execution
Visuomotor Tracking Task for Enhancing Activity in Motor Areas of Stroke Patients
Recovery of motor function following stroke requires interventions to enhance ipsilesional cortical activity. To improve finger motor function following stroke, we developed a movement task with visuomotor feedback and measured changes in motor cortex activity by electroencephalography. Stroke patients performed two types of movement task on separate days using the paretic fingers: a visuomotor tracking task requiring the patient to match a target muscle force pattern with ongoing feedback and a simple finger flexion/extension task without feedback. Movement-related cortical potentials (MRCPs) were recorded before and after the two motor interventions. The amplitudes of MRCPs measured from the ipsilesional hemisphere were significantly enhanced after the visuomotor tracking task but were unchanged by the simple manual movement task. Increased MRCP amplitude preceding movement onset revealed that the control of manual movement using visual feedback acted on the preparatory stage from motor planning to execution. A visuomotor tracking task can enhance motor cortex activity following a brief motor intervention, suggesting efficient induction of use-dependent cortical plasticity in stroke
Gating of somatosensory evoked magnetic fields and potentials during the preparatory period of self-initiated voluntary movement
Gating of somatosensory evoked magnetic fields and potentials during the preparatory period of self-initiated voluntary movement
ヒトは皮膚を通して外界の情報を,筋・腱からは身体内部の状態に関する情報を,時々刻々と脳にフィードバックしている.これらの感覚情報は総称して「体性感覚」と呼ばれており,触覚,圧覚,振動覚などの「皮膚感覚」と運動感覚や位置覚などの「深部感覚」に区別される.この体性感覚情報は,随意運動の遂行に重要な役割を担っている.ヒトの随意運動の遂行に関連する体性感覚系に変化については,体性感覚誘発電位(SEPs)や体性感覚誘発脳磁図(SEFs)を用いて非侵襲的に研究が盛んに行われてきた.SEPsやSEFsの振幅は,運動の遂行の影響を受けて減少し,これは一般的に‘gating’と呼ばれている.このgatingは能動的収縮時,受動的収縮時や触覚の干渉刺激時にみられることが多数の先行研究で報告されている. 随意運動を円滑に遂行するためには,運動の内容を組立て企画する準備期が重要な働きを担っているが,この準備期における体性感覚系の変動については不明な点が多く残されている.これまでにも,随意運動前の体性感覚系の変動に関する報告はみられるが,そのほとんどは反応動作課題を用いたものであった.しかし,この反応動作課題は反応信号を用いるため,反応信号に対する注意や期待などの要因が体性感覚系に作用することが考えられる.そのため,体性感覚系が準備期のどの段階から運動出力系の影響(centrifilgal gating)を受けて変動がみられるかを詳細に調べることができなかった.そこで本研究は反応信号を用いず,被験者が自己ペースで随意運動を発現させる「自発運動」を用いて,その準備期における体性感覚系の変動をSEPsとSEFsを用いて検討した. 随意運動の準備期にみられるSEPs/SEFsのgatingは,筋放電に伴う求心性情報の上行による干渉作用(centripetal gating)の影響を除外できるため,運動関連領域から体性感覚系に対する修飾(centrifugal gating)が原因であると考えられる.そこで,最初の実験では,この運動関連領域からのcentrifugal gatingを検証するために,自発運動の準備期に頭皮上から記録される運動関連脳電位(MRCPs)とSEPsを同時に測定した.MRCPsは随意運動の準備期における運動関連領域の活動を反映しており,準備期にみられるSEPs/SEFsが,運動関連領域からの影響を受けるのであれば,SEPs/SEFsはMRCPsと関連して変動することが想定される.そこで,下肢の自発的底屈動作の準備期について,MRCPsの構成成分であるBereitschaftspotentialとNegative slopeを基準とした6区間(NS\u27-1,NS\u27-2,BP-1,BP-2,BP-3,Pre-BP)におけるSEPsの変動を調べた.SEPsを誘発するための電気刺激は,右脚の膝窩部に刺激頻度1~3Hzでランダムに呈示し,被験者にはこの電気刺激を無視して自発的な底屈動作を行うように指示した.全被験者について,Czで最大のSEP波形が確認され,P30,N40,P53,N70成分が同定された.準備期に有意なSEPs振幅の変動(gating)がみられたのはN40成分のみであった.N40成分の振幅は,MRCPsが出現するBP-3区間から有意な低下がみられ,MRCPsの振幅が急激に増大するNS\u27-1区間で大きく減少することが確認された.以上の結果から,自発運動前のSEPsは運動関連領域の影響を受けていること(centrifugal gating)が強く示唆された. 次に,脳波よりも電位の発生源の推定精度が高い脳磁図を用いて,第二指の自発的伸展動作の準備期におけるSEFsを測定し,各成分における双極子(dipole)の位置と強さ(dipole moment)を計算した.SEFsを誘発するための電気刺激は,右手首の正中神経に刺激間間隔600~800msの間でランダムに呈示し,被験者にはその電気刺激を無視して5-7秒間隔で自発的な指伸展を行わせた.本実験においては,随意運動の準備期を全被験者について同一の区間に分割した.その区間は,筋放電の立ち上がりからその前500ms(0ms~-500ms),-500ms~-1000ms,-1000ms~-1500ms,-1500ms~-2000ms,-2000ms~-3000ms,-3000ms~-4000msとした.明瞭なSEPs波形は,刺激と対側半球の中心部に明瞭な磁場成分がみられ,N20m,P30m,P60m成分が確認された.これらの3成分から推定されたdipoleの位置は,いずれも中心溝後壁の一次体性感覚野近辺であった.安静条件と随意運動の準備期における各成分のdipole momentを比較すると,P30m成分のみに有意な変動が認められ,筋放電から500ms前の区間(0ms~-500ms)でdipole momentの減少(gating)がみられた.また-3000ms~-4000msの区間におけるP30m成分のdipole momentと比較すると,1500ms以降の区間(0ms~-1500ms)で有意な減少が確認された. 本研究から,上肢,下肢ともに単関節における素早い自発運動の準備期には,少なくとも筋放電の500ms前から体性感覚系に変動がみられることが示された.随意運動の準備期には筋放電がみられないため,求心性情報による干渉作用(centripetal gating)の影響は無視できると考えられる.自発運動の準備期には補足運動野や一次運動野に活動がみられるため,準備期にみられるSEPs/SEFsのgatingは,運動関連領域から一次体性感覚野への抑制性投射(centrifugal gating)が原因であると考えられる.また,この抑制性投射の影響は,一次体性感覚野のすべての領域に対して一様に作用するのではなく,ある領域に対して特異的に作用することが示唆される
Time-Varying Cortical Activations Related to Visual–Tactile Cross-Modal Links in Spatial Selective Attention
Differential influences of exercise intensity on information processing in the central nervous system
The Sequence Effect in Parkinson’s Disease
Background and Purpose The sequence effect (SE) in Parkinson’s disease (PD) denotes progressive slowness in speed or progressive decrease in amplitude of repetitive movements. It is a well-known feature of bradykinesia and is considered unique in PD. Until now, it was well-documented in advanced PD, but not in drug-naïve PD. The aim of this study is to know whether the SE can also be measured in drug-naïve PD. Methods We measured the SE with a computer-based, modified Purdue pegboard in 4 drug-naïve PD patients, which matched our previous study with advanced PD patients. Results We observed progressive slowness during movement, that is, SE. Statistical analysis showed a strong statistical trend toward the SE with the right hand, but no significance with the left hand. There was no statistical significance of SE with either the more or less affected hands. Conclusions These results indicate that the SE can be identified in drug-naïve PD, as well as in advanced PD, with objective measurements and support the idea that the SE is a feature in PD observed during the early stage of the disease without medication
The cerebral representation of scratching-induced pleasantness
Itch is an unpleasant sensation with the desire to scratch. Although it is well known that scratching itchy skin is pleasurable, the cerebral mechanisms underlying this phenomenon are poorly understood. We hypothesized that the reward system is associated with scratching-induced pleasantness. To investigate this hypothesis, a functional magnetic resonance imaging study was performed in 16 healthy subjects. Pleasantness was evoked by scratching the wrists where itch stimuli were applied, while scratching the dorsal forearms, far from itch stimuli, did not evoke pleasantness. Interestingly, pleasantness evoked by scratching activated not only the reward system (i.e., the striatum and midbrain) but also key regions of perception (i.e., the primary somatosensory cortex) and awareness of subjective feelings (i.e., the insular cortex), indicating that a broad network is involved in scratching-induced pleasantness. Moreover, although itch was suppressed by scratching, motor-related regions such as the supplementary motor area, premotor cortex, and cerebellum showed significant activation when pleasantness was evoked. This activation could explain why scratching-induced pleasantness potentially reinforces scratching behaviors. This study is the first to identify networks activated by scratching-induced pleasantness. The results of the present study provide important information on the cerebral mechanisms underlying why scratching itchy skin evokes pleasurable feelings that reinforce scratching behaviors