Magnetoencephalographic study of event‐related fields and cortical oscillatory changes during cutaneous warmth processing

Thermoreception is an important cutaneous sense, which plays a role in the maintenance of our body temperature and in the detection of potential noxious heat stimulation. In this study, we investigated event‐related fields (ERFs) and neural oscillatory activities, which were modulated by warmth stimulation. We developed a warmth stimulator that could elicit a warmth sensation, without pain or tactile sensation, by using a deep‐penetrating 980‐nm diode laser. The index finger of each participant (n = 24) was irradiated with the laser warmth stimulus, and the cortical responses were measured using magnetoencephalography (MEG). The ERFs and oscillatory responses had late latencies (～1.3 s and 1.0–1.5 s for ERFs and oscillatory responses, respectively), which could be explained by a slow conduction velocity of warmth‐specific C‐fibers. Cortical sources of warmth‐related ERFs were seen in the bilateral primary and secondary somatosensory cortices (SI and SII), posterior part of the anterior cingulate cortex (pACC), ipsilateral primary motor, and premotor cortex. Thus, we suggested that SI, SII, and pACC play a role in processing the warmth sensation. Time–frequency analysis demonstrated the suppression of the alpha (8–13 Hz) and beta (18–23 Hz) band power in the bilateral sensorimotor cortex. We proposed that the suppressions in alpha and beta band power are involved in the automatic response to the input of warmth stimulation and sensorimotor interactions. The delta band power (1–4 Hz) increased in the frontal, temporal, and cingulate cortices. The power changes in delta band might be related with the attentional processes during the warmth stimulation.     

Attention modulates beta oscillations during prolonged tactile stimulation

The inter‐play between changes in beta‐band (14–30‐Hz) cortical rhythms and attention during somatosensation informs us about where and when relevant processes occur in the brain. As such, we investigated the effects of attention on somatosensory evoked and induced responses using vibrotactile stimulation and magnetoencephalographic recording. Subjects received trains of vibration at 23 Hz to the right index finger while watching a movie and ignoring the somatosensory stimuli or paying attention to the stimuli to detect a change in the duration of the stimulus. The amplitude of the evoked 23‐Hz steady‐state response in the contralateral primary somatosensory cortex (SI) was enhanced by attention and the underlying dipole source was located 2 mm more medially, indicating top‐down recruitment of additional neuronal populations for the functionally relevant stimulus. Attentional modulation of the somatosensory evoked response indicates facilitation of early processing of the tactile stimulus. Beta‐band activity increased after vibration offset in the contralateral primary motor cortex (MI) [event‐related synchronization (ERS)] and this increase was larger for attended than ignored stimuli. Beta‐band activity decreased in the ipsilateral SI prior to stimulus offset [event‐related desynchronization (ERD)] for attended stimuli only. Whereas attention modulation of the evoked response was confined to the contralateral SI, event‐related changes of beta‐band activity involved contralateral SI–MI and inter‐hemispheric SI–SI connections. Modulation of neural activity in such a large sensorimotor network indicates a role for beta activity in higher‐order processing.     

Effects of muscle contraction on somatosensory event-related EEG power and coherence changes.

Effects of isometric muscle contraction on amplitude and coherence changes of EEG rhythms during repetitive cutaneous electrical stimulation were analyzed in 10 right-handed subjects. Subjects received electrical stimuli at intensity above pain threshold to their right middle finger while either squeezing a rubber tube with the right index finger and thumb, or keeping their ipsilateral hand muscles relaxed. EEG was recorded using 111 closely spaced electrodes. Somatosensory stimuli were followed by reduction of the relative 8-12 and 16-24 Hz band power (at 0.2-0.4 s) in bilateral primary sensorimotor cortices (S1/M1) and medial frontal cortex, and by a subsequent increase in 16-24 Hz band power (at 0.9 s). Isometric muscle contraction strongly suppressed these band power changes. The 8-12 and 16-24 Hz mean coherence in a wide region surrounding the contralateral S1/M1 and in the medial frontal cortex showed an initial decrease, partially paralleling band power changes, and later an increase. Ipsilateral S1/M1 showed a decrease in 8-12 Hz coupling only with the central and frontal electrodes of the same hemisphere. Muscle contraction reduced all coherence changes, but enhanced the 8-12 Hz coherence between ipsilateral S1/M1 and posterior parietal cortex. Early post-stimulus decrease of oscillatory coupling between S1/M1 and premotor cortex and between S1/M1 and medial frontal cortex suggests that these cortical regions act rather independently during processing of somatosensory information, and synchronize only later when the band power in contralateral S1/M1 increases. Motor cortex activation associated with ipsilateral hand muscle contraction interferes with cortical processing of somatosensory stimuli in S1/M1 cortices.     

Oscillatory response function: Towards a parametric model of rhythmic brain activity

Rhythmic brain activity, measured by magnetoencephalography (MEG), is modulated during stimulation and task performance. Here, we introduce an oscillatory response function (ORF) to predict the dynamic suppression–rebound modulation of brain rhythms during a stimulus sequence. We derived a class of parametric models for the ORF in a generalized convolution framework. The model parameters were estimated from MEG data acquired from 10 subjects during bilateral tactile stimulation of fingers (stimulus rates of 4 Hz and 10 Hz in blocks of 0.5, 1, 2, and 4 s). The envelopes of the 17–23 Hz rhythmic activity, computed for sensors above the rolandic region, correlated 25%–43% better with the envelopes predicted by the models than by the stimulus time course (boxcar). A linear model with separate convolution kernels for onset and offset responses gave the best prediction. We studied the generalizability of this model with data from 5 different subjects during a separate bilateral tactile sequence by first identifying neural sources of the 17–23 Hz activity using cortically constrained minimum norm estimates. Both the model and the boxcar predicted strongest modulation in the primary motor cortex. For short‐duration stimulus blocks, the model predicted the envelope of the cortical currents 20% better than the boxcar did. These results suggest that ORFs could concisely describe brain rhythms during different stimuli, tasks, and pathologies. Hum Brain Mapp, 2010. © 2009 Wiley‐Liss, Inc.     

Cortical activity to vibrotactile stimulation: an fMRI study in blind and sighted individuals

Blind individuals show visual cortex activity during Braille reading. We examined whether such cross-modal activations reflect processing somatosensory stimuli independent of language by identifying cortical activity during a one-back vibrotactile matching task. Three groups (sighted, early-onset, and late-onset [>12 years] blind) detected whether paired vibrations (25 and 100 Hz), delivered to the right index finger, differed in frequency. Three successive paired vibrations, followed by a no-stimulation interval, were presented in a long event-related design. A fixed effects average z-score analysis showed increased activity throughout the visuotopic visual cortex, where it was mostly restricted to foveal and parafoveal eccentricities. Early blind showed the most extensive distribution of activity. Late blind exhibited activity mostly in similar regions but with declining response magnitudes with age of blindness onset. Three sighted individuals had suprathreshold activity in V1 but negative responses elsewhere in visual cortex. Mixed effects ANOVA confirmed group distinctions in defined regions (V1, V3, V4v, V7, LOC, and MT). These results suggest cross-modal adaptation to tactile stimulation in visual cortex independent of language processes. All groups showed increased activity in left primary (S1) and bilateral second somatosensory areas, but without response magnitude differences between groups throughout sensorimotor cortex. Early blind showed the greatest spatial extent of S1 activity. Blind participants had more extensive bilateral activity in anterior intraparietal sulcus and supramarginal gyrus. Extensive usage of touch in Braille reading may underlie observed S1 expansions in the reading finger representation. In addition, learned attentiveness to touch may explain similar expansion of parietal tactile attention regions.     

Anticipation of somatosensory and motor events increases centro-parietal functional coupling: an EEG coherence study.

OBJECTIVE: Does functional coupling of centro-parietal EEG rhythms selectively increase during the anticipation of sensorimotor events composed by somatosensory stimulation and visuomotor task? METHODS: EEG data were recorded in (1) 'simultaneous' condition in which the subjects waited for somatosensory stimulation at left hand concomitant with a Go (or NoGo) visual stimulus triggering (50%) right hand movements and in (2) 'sequential' condition where the somatosensory stimulation was followed (+1.5 s) by a visuomotor Go/NoGo task. Centro-parietal functional coupling was modeled by spectral coherence. Spectral coherence was computed from Laplacian-transformed EEG data at delta-theta (2-7 Hz), alpha (8-14 Hz), beta 1 (15-21 Hz), beta 2 (22-33 Hz), and gamma (34-45 Hz) rhythms. RESULTS: Before 'simultaneous' sensorimotor events, centro-parietal coherence regions increased in both hemispheres and at all rhythms. In the 'sequential' condition, right centro-parietal coherence increased before somatosensory event (left hand), whereas left centro-parietal coherence increased before subsequent Go/NoGo event (right hand). CONCLUSIONS: Anticipation of somatosensory and visuomotor events enhances contralateral centro-parietal coupling of slow and fast EEG rhythms. SIGNIFICANCE: Predictable somatosensory and visuomotor events are anticipated not only by synchronization of cortical pyramidal neurons generating EEG power in parietal and primary sensorimotor cortical areas (Babiloni C, Brancucci A, Capotosto P, Arendt-Nielsen L, Chen ACN, Rossini PM. Expectancy of pain is influenced by motor preparation: a high-resolution EEG study of cortical alpha rhythms. Behav. Neurosci. 2005a;119(2):503-511; Babiloni C, Brancucci A, Pizzella V, Romani G.L, Tecchio F, Torquati K, Zappasodi F, Arendt-Nielsen L, Chen ACN, Rossini PM. Contingent negative variation in the parasylvian cortex increases during expectancy of painful sensorimotor events: a magnetoencephalographic study. Behav. Neurosci. 2005b;119(2):491-502) but also by functional coordination of these areas.     

Relationship between intracerebral gamma oscillations and slow potentials in the human sensorimotor cortex

Changes in sensorimotor rhythms (mu, beta and gamma) and movement-related cortical potentials (MRCPs) are both generated principally by the contralateral sensorimotor areas during the execution of self-paced movement. They appear to reflect movement control mechanisms, which remain partially unclear. With the aim of better understanding their sources and significance, we recorded MRCPs and sensorimotor rhythms during and after self-paced movement using intracerebral electrodes in eight epileptic subjects investigated by stereoelectroencephalography. The results showed that: (i) there is a strong spatial relationship between the late components of movement--the so-called motor potential (MP) and post-movement complex (PMc)--and gamma event-related synchronization (ERS) within the 40-60 Hz band, as the MP/PMc always occurred in contacts displaying gamma ERS (the primary sensorimotor areas), whereas mu and beta reactivities were more diffuse; and (ii) MPs and PMc are both generated by the primary motor and somatosensory areas, but with distinct sources. Hence, this could mean that kinesthesic sensory afferences project to neurons other than those firing during the pyramidal tract volley. The PMc and low gamma ERS represent two electrophysiological facets of kinesthesic feedback from the joints and muscles involved in the movement to the sensorimotor cortex. It could be suggested that gamma oscillations within the 40-60 Hz band could serve to synchronize the activities of the various neuronal populations involved in control of the ongoing movement.     

Neuromagnetic functional coupling during dichotic listening of speech sounds

The present magnetoencephalography (MEG) study tested the hypothesis of a phase synchronization (functional coupling) of cortical alpha rhythms (about 6-12 Hz) within a "speech" cortical neural network comprising bilateral primary auditory cortex and Wernicke's areas, during dichotic listening (DL) of consonant-vowel (CV) syllables. Dichotic stimulation was done with the CV-syllable pairs /da/-/ba/ (true DL, yielded by stimuli having high spectral overlap) and /da/-/ka/ (sham DL, obtained with stimuli having poor spectral overlap). Whole-head MEG activity (165 sensors) was recorded from 10 healthy right-handed non-musicians showing right ear advantage in a speech DL task. Functional coupling of alpha rhythms was defined as the spectral coherence at the following bands: alpha 1 (about 6-8 Hz), alpha 2 (about 8-10 Hz), and alpha 3 (about 10-12) with respect to the peak of individual alpha frequency. Results showed an inverse pattern of functional coupling: during DL of speech sounds, spectral coherence of the high-band alpha rhythms increased between left auditory and Wernicke's areas with respect to sham DL, whereas it decreased between left and right auditory areas. The increase of functional coupling within the left hemisphere would underlie the processing of the syllable presented to the right ear, which arrives to the left auditory cortex without the interference of the other syllable presented to the left ear. Conversely, the decrease of inter-hemispherical coupling of the high-band alpha might be due to the fact that the two auditory cortices do not receive the same information from the ears during DL. These results suggest that functional coupling of alpha rhythms can constitute a neural substrate for the lateralization of auditory stimuli during DL.     

Event-related changes in neuromagnetic activity associated with syncopation and synchronization timing tasks

For low rhythmic rates (1.0 to approximately 2.0 Hz), subjects are able to successfully coordinate finger flexion with an external metronome in either a syncopated (between the beats) or synchronized (on each beat) fashion. Beyond this rate, however, syncopation becomes unstable and subjects spontaneously switch to synchronization to maintain a 1:1 stimulus/response relationship. We used a whole-head magnetometer to investigate the spatiotemporal dynamics of neuromagnetic activity (MEG) associated with both coordinative patterns at eight different rates spanning the range 1.0-2.75 Hz. Timing changes in the event-related fields accompanied transitions from syncopation to synchronization and followed the placement of the motor response within each stimulus/response cycle. Decomposition of event-related fields into component auditory and motor brain responses revealed that the amplitude of the former decreased with increasing coordination rate whereas the motor contribution remained approximately constant across all rates. Such an interaction may contribute to changes in auditory-motor integration that cause syncopation to become unstable. Examination of event-related changes in high frequency bands revealed that MEG signal power in the beta band (15-30 Hz) was significantly lower during syncopated coordination in sensors covering the contralateral sensorimotor area suggesting a dependence of beta rhythm amplitude on task difficulty. Suppression of beta rhythms was also stronger during synchronization preceded by syncopation, e.g., after subjects had switched, when compared with a control condition in which subjects synchronized throughout the entire range of rates.     

Cerebral motor control in patients with gliomas around the central sulcus studied with spatially filtered magnetoencephalography

OBJECTIVE: Application of spatially filtered magnetoencephalography (MEG) to investigate changes in the mechanism of cerebral motor control in patients with tumours around the central sulcus. METHODS: MEG records were made during a repetitive hand grasping task in six patients with gliomas around the central sulcus and in four control subjects. Power decreases in the alpha (8-13 Hz), beta (13-30 Hz), and low gamma bands (30-50 Hz) during the motor tasks (event related desynchronisation, ERD) were analysed statistically with synthetic aperture magnetometry. The tomography of ERD was superimposed on the individual's magnetic resonance image. RESULTS: beta ERD was consistently localised to the contralateral primary sensorimotor cortex (MI/SI) in control subjects, whereas the alpha and low gamma ERD showed considerable intersubject variability. beta ERD in patients during non-affected side hand movement was also localised to the contralateral MI/SI, but exclusively to the ipsilateral hemisphere during affected side hand movement. CONCLUSIONS: The altered pattern of ERD in the patient group during affected side hand movement suggests recruitment of diverse motor areas, especially the ipsilateral MI/SI, which may be required for the effective movement of the affected hand.     

Behavioral significance of input-dependent plasticity of human somatosensory cortex

Training and learning induce powerful cortical reorganizational changes, which are referred to as use- or experience-dependent plasticity. Using MEG, we investigated how rapid reorganization of human somatosensory cortex induced by tactile stimulation leads to improved spatial discrimination performance. Plastic changes were induced by several hours of tactile co-activation in separated receptive fields on the right index finger. Subjects did not attend the stimulation but performed their daily work. We found a 20% decrease in spatial two-point discrimination thresholds paralleled by a dipole shift in medio-lateral direction along the central sulcus. We conclude that reorganization of primary somatosensory cortex induced by purely passive tactile co-activation is sufficient to improve tactile discrimination performance without training, attention or reinforcement.     

Pulmonary vagal sensory afferents and spontaneous EEG rhythms in the cat sensorimotor cortex

Interactions between vagal afferent fibres and spontaneous electroencephalographic (EEG) activity, recorded on the sensorimotor cortex of the cat, were studied during the mechanical activation of pulmonary afferents. The interactions were compared to the cortical effects of the electrical stimulation of all vagal fibers or to the chemical activation of unmyelinated vagal afferents (C-fibers) by phenyldiguanide. The present study was performed on anesthetized cats, artificially ventilated with open chest. Over 60 locations were explored on the posterior sigmoid gyrus. Repetitive electrical stimulation (30 Hz, 0.8 ms shock duration) of the contralateral cervical vagus nerve or of both nerves induced within less than 5 s changes in the pattern and periodicity of EEG spindles, associated with depressed background rhythms or rhythmic EEG activities. Cortical responses were also observed after i.v. injection of phenyldiguanide. Changes in activity of pulmonary stretch receptors by lung hyperinflation or suppression of phasic lung inflations ('stop pump') had no effect on the EEG rhythms. On the other hand, expiratory threshold loading or passive hyperdeflation of the lungs elicited EEG changes similar to those obtained by electrical stimulation of all vagal fibers. After bilateral vagotomy, all these responses disappeared or were delayed. The present observations strongly suggest that sensory information carried by thin vagal fibers greatly influences cortical rhythms in the cat sensorimotor cortex.     

Ipsilateral cortical activation in fibromyalgia patients during brushing correlates with symptom severity

ObjectiveTo evaluate cortical activation patterns during mechanical-tactile stimulation in fibromyalgia syndrome (FMS) patients and to correlate cortical activation changes with clinical symptoms.MethodsNineteen female FMS patients and 18 matched, healthy control subjects underwent EEG examination during brushing stimulation of the right forearm. Participants rated any pain experienced and underwent a manual tender point scale (MTPS) examination. Amplitude changes of cortical rhythms during brushing were analysed in alpha (8–13 Hz) and beta (16–24 Hz) frequency bands.ResultsThirteen patients reported pain during brushing. Independent t-test comparison of event related desynchronisation (ERD) during brushing revealed a cluster of electrodes over ipsilateral (right) central–parietal region which demonstrated ERD in patients only. Clinical MTPS scores correlated with beta-band ERD in this cluster of electrodes. Beamformer analysis revealed a widespread array of source activations in patients, including bilateral insula and primary and secondary somatosensory cortices. Control subject source activations were limited to contralateral (left) hemisphere.ConclusionsResults indicate ipsilateral cortical activations in FMS patients, but not in healthy controls, during brushing. Ipsilateral ERD during brushing is associated with MTPS score suggesting abnormal processing of somatosensory input which may contribute to clinical pain.SignificanceAltered functioning in FMS may reflect physiological changes in response to afferent somatosensory information manifesting in chronic pain.     

Changes in cortical oscillations linked to multisensory modulation of nociception

Pain can be modulated by several contextual factors. For example, simply viewing one's own body can reduce pain, suggesting that the visual context may influence the processing of nociceptive stimuli. We studied changes in electroencephalographic (EEG) oscillatory activity related to visual modulation of nociception, comparing cortical oscillations during innocuous or noxious contact heat, while participants viewed either their own hand or a neutral object at the same location. Viewing the body compared with viewing the object reduced the intensity ratings of noxious stimuli, but not of innocuous heat. Time–frequency analysis of EEG data revealed that noxious, as opposed to warm, stimulation was associated with reduced beta (15–25 Hz) power. Classically, such decreases in oscillatory power indicate increases in sensory cortical activation. These event‐related oscillatory changes were moreover modulated by the visual context; viewing one's own body increased noxious stimulation‐induced beta oscillatory activity bilaterally, relative to viewing a neutral object, possibly indicating inhibition of cortical nociceptive processing. These results demonstrate that visual–nociceptive interactions involve changes in sensorimotor EEG rhythms.     

Task-related coherence and task-related spectral power changes during sequential finger movements

In order to investigate the activity of cortical regions in the control of complex movements, we studied task-related coherence (TRCoh) and task-related spectral power (TRPow) changes in 8 right-handed subjects during the execution of 4 different finger movement sequences of increasing complexity. All sequences were performed with the right hand and were paced by a metronome at 2 Hz. EEG power spectra and coherence values were computed within alpha (8-12 Hz) and beta (13-20 Hz) frequency bands for 29 scalp EEG positions during the execution of the sequences and were compared with values obtained during a rest (control) condition. Movement sequences were associated with TRPow decreases in the alpha and beta frequency bands over bilateral sensorimotor and parietal areas, with a preponderance over the contralateral hemisphere. Increases of TRCoh occurred over bilateral frontocentral regions. TRCoh decreases were present over the temporal and occipital areas. The spatial extent and the magnitude of TRPow decreases and TRCoh increases in both frequency bands were greater for sequential movements of higher complexity than for simpler ones. These results are consistent with previous findings of bilateral activation of sensorimotor areas during sequential finger movements. Moreover, the present results indicate an active intercommunication between bilateral and mesial central and prefrontal regions which becomes more intense with more complex sequential movements.     

Gamma synchronization in human primary somatosensory cortex as revealed by somatosensory evoked neuromagnetic fields

Cortical sensory neurons synchronize their activity at multiple frequency bands after an external stimulation. In the somatosensory cortical areas, previous reports describe more discrete and somatotopically specific neural synchronization at the gamma band. Therefore, an efficient gamma synchronization of the neurons in primary somatosensory cortex (S1) may be expected to characterize the stimulus processing from the thumb, i.e. the hand's most skillful area. To test this hypothesis, neuromagnetic fields were evoked over human S1 by the electrical stimulation of the contralateral thumb or little finger. Neuronal synchronization was indexed by the spectral coherence of the evoked neuromagnetic fields overlying S1. The frequencies of interest were the beta (16-32 Hz) and gamma (36-46 Hz) bands. The global amount of the coherence was defined as the total event-related coherence (ERCoh) among all magnetic sensors overlying the S1. Results showed prevalent increment of beta ERCoh (20-32 Hz) after the little finger stimulation and of gamma ERCoh (36-44 Hz) after the thumb stimulation. These results suggest that the neural synchronization in S1, as revealed by the ERCoh, may vary in frequency as a function of the finger stimulated. In this framework, the neural synchronization at gamma band may characterize the cortical representation of thumb, functionally prevalent with respect to little finger in humans.     

Acute modulation of cortical oscillatory activities during short trains of high-frequency repetitive transcranial magnetic stimulation of the human motor cortex: a combined EEG and TMS study

In this study, a combined repetitive transcranial magnetic stimulation/electroencephalography (rTMS/EEG) method was used to explore the acute changes of cortical oscillatory activity induced by intermittent short trains of high-frequency (5-Hz) rTMS delivered over the left primary motor cortex (M1). We evaluated the electrophysiological reaction to magnetic stimulation during and 2-4 s after 20 trains of 20-pulses rTMS, using event-related power (ERPow) that reflects the regional oscillatory activity of neural assemblies, and event-related coherence (ERCoh) that reflects the interregional functional connectivity of oscillatory neural activity. These event-related transformations were for the upper alpha (10-12 Hz) and beta (18-22 Hz) frequency ranges, respectively. For the alpha band, threshold rTMS and subthreshold rTMS induced an ERPow increase during the trains of stimulation mainly in frontal and central regions ipsilateral to stimulation. For the beta band, a similar synchronization of cortical oscillations for both rTMS intensities was seen. Moreover, subthreshold rTMS affected alpha-band activity more than threshold rTMS, inducing a specific ERCoh decrease over the posterior regions during the trains of stimulation. For beta band, the decrease in functional coupling was observed mainly during threshold rTMS. These findings provide a better understanding of the cortical effects of high-frequency rTMS, whereby the induction of oscillations reflects the capacity of electromagnetic pulses to alter regional and interregional synaptic transmissions of neural populations.     

Beta‐band oscillations play an essential role in motor–auditory interactions

In the human brain, self‐generated auditory stimuli elicit smaller cortical responses compared to externally generated sounds. This sensory attenuation is thought to result from predictions about the sensory consequences of self‐generated actions that rely on motor commands. Previous research has implicated brain oscillations in this process. However, the specific role of these oscillations in motor–auditory interactions during sensory attenuation is still unclear. In this study, we aimed at addressing this question by using magnetoencephalography (MEG). We recorded MEG in 20 healthy participants during listening to passively presented and self‐generated tones. Our results show that the magnitude of sensory attenuation in bilateral auditory areas is significantly correlated with the modulation of beta‐band (15–30 Hz) amplitude in the motor cortex. Moreover, we observed a significant directional coupling (Granger causality) in beta‐band originating from the motor cortex toward bilateral auditory areas. Our findings indicate that beta‐band oscillations play an important role in mediating top–down interactions between motor and auditory cortex and, in our paradigm, suppress cortical responses to predicted sensory input.     

Functional changes of the cortical motor system in hereditary spastic paraparesis

Background – Hereditary spastic paraparesis (HSP) is a heterogeneous group of disorders characterized by progressive bilateral lower limb spasticity. Functional imaging studies in patients with corticospinal tract involvement have shown reorganization of motor circuitry. Our study investigates functional changes in sensorimotor brain areas in patients with HSP. Methods – Twelve subjects with HSP and 12 healthy subjects were studied. Functional magnetic resonance imaging (fMRI) was used to measure brain activation during right‐hand finger tapping. Image analysis was performed using general linear model and regions of interest (ROI)‐based approach. Weighted laterality indices (wLI) and anterior/posterior indicies (wAI and wPI) were calculated for predefined ROIs. Results and discussion – Comparing patients and controls at the same finger‐tapping rate (1.8 Hz), there was increased fMRI activation in patients’ bilateral posterior parietal cortex and left primary sensorimotor cortex. No differences were found when comparing patients and controls at 80% of their individual maximum tapping rates. wLI of the primary sensorimotor cortex was significantly lower in patients. Subjects with HSP also showed a relative increase in the activation of the posterior parietal and premotor areas compared with that of the primary sensorimotor cortex. Our findings demonstrate an altered pattern of cortical activation in subjects with HSP during motor task. The increased activation probably reflects reorganization of the cortical motor system.     

The influence of normal aging on the cortical processing of a simple motor task

OBJECTIVE: To assess the influence of normal aging on the cortical physiology of motor behavior. METHODS: The authors studied cortical activation in eight elderly (55 to 76 years of age) and eight younger (18 to 27 years of age) healthy subjects while they performed a simple motor task. A 28-channel EEG was recorded; task-related power changes associated with repetitive, metronome-paced (1 Hz) finger movements were computed as a measure of cortical activation. RESULTS: Distinct, age-dependent activation patterns were expressed in four distinct frequency ranges: low-alpha (10 to 11 Hz), high-alpha (12 to 13 Hz), low-beta (16 to 17 Hz), and high-beta (22 to 23 Hz) bands. The main findings were a greater overall activation and, more specifically, a pronounced bilateral activation of sensorimotor regions in elderly subjects for both alpha bands. Additionally, in the elderly subjects there was increased activation of the mesial frontocentral cortex (supplementary motor area region) in the high-beta band, whereas younger volunteers had a prominent activation of the left lateral premotor and sensorimotor region in this frequency range. CONCLUSIONS: These findings demonstrate that the functional anatomy of the human motor system changes during normal aging. It appears that, for a given motor task, the aging brain recruits additional primary sensorimotor and premotor regions of both hemispheres.