Biomedical subjects

J Liepert

Publications and source records attributed to J Liepert.

At least 37 records · Page 2Linked to original sources

PubMed2001

Motor cortex disinhibition in Alzheimer's disease.

OBJECTIVES: To explore subclinical disturbances in the motor cortex of patients with Alzheimer's disease (AD). METHODS: We used transcranial magnetic stimulation in a paired pulse technique to test intracortical inhibition (ICI) and intracortical facilitation in mildly to moderately demented AD patients with a normal neurological examination. Patients were studied before and during treatment with the cholinesterase inhibitor donepezil. RESULTS: AD patients had a reduced ICI compared to an age-matched control group. The amount of disinhibition correlated with the severity of dementia. Treatment with 10 mg donepezil daily was associated with an increase of ICI. CONCLUSIONS: The subclinical motor cortex disinhibition in AD patients indicates a functional disturbance, and is probably associated with a cholinergic deficit.

Aged↗

PubMed2000

The influence of lorazepam on somatosensory-evoked fast frequency (600 Hz) activity in MEG.

The generators of high frequency bursts (600-Hz activity) detected at the parietal scalp over the primary somatosensory cortex after electrical stimulation of peripheral nerves are not yet known. We investigated the influence of benzodiazepine on the somatosensory-evoked 600-Hz activity by means of neuromagnetic measurements and source analysis. After oral administration of lorazepam, the latency of the 600-Hz burst activity was increased; specifically later peaks were delayed more than earlier peaks. In contrast, the latency of the concurrent primary cortical low frequency response (N20m) was not significantly changed. The source strengths of both N20m and 600-Hz bursts were significantly increased. Our results provide evidence for two components of the 600-Hz activity with a different generator structure.

Adult↗

PubMed2000

Effects of passive tactile co-activation on median ulnar nerve representation in human SI.

In animals simple passive co-activation causes a fusion and expansion of the involved cortical representations. We used passive tactile finger co-activation for 40 min to investigate cortical representational changes in the human somatosensory cortex. Magnetic source imaging revealed that the euclidean distance between median and ulnar nerve somatosensory evoked fields (SEF) was significantly reduced after application of 600 synchronous airpuff stimuli to the fingertips of four fingers. In the control experiment without co-activation no significant change in distance was observed. Perception threshold and spatial two-point discrimination were not affected by the synchronous stimulation. This is in contrast to blind three-finger Braille readers who frequently mislocalize stimuli applied to the reading fingers. This points to a lack of behavioural relevance or the short duration of co-activation.

Adult↗

PubMed2000

Motor cortex disinhibition of the unaffected hemisphere after acute stroke.

We studied motor cortex excitability in the nonlesioned hemisphere of patients with a large cortical infarction. Patients with a severe hemiparesis due to a stroke were compared with age-matched, healthy controls. Paired transcranial magnetic stimuli were applied over the unaffected hemisphere to investigate intracortical inhibition and facilitation. In the patient group, intracortical inhibition was reduced. We suggest that this disinhibition is due to an impairment of transcallosal fibers and may affect recovery.

Acute Disease↗

PubMed2000

Riluzole suppresses motor cortex facilitation in correlation to its plasma level. A study using transcranial magnetic stimulation.

The aim of our study was to measure the effects of the glutamate antagonist riluzole on different parameters of motor excitability, using transcranial magnetic stimulation (TMS) during 7 days of riluzole administration, and to correlate these effects with riluzole plasma levels. Nine healthy volunteers received a dose of 100 mg riluzole from day 1 to 7 of the study period. Electrophysiological examinations were performed on day 1 before and 2 h, 5 h and 8 h after riluzole administration, on day 2, day 3 and day 5 before riluzole administration, and on day 8. Plasma samples were taken simultaneously. The excitability of the motor cortex, supraspinal and spinal motor pathways was tested by studying intracortical facilitation and inhibition, the cortical silent period and motor threshold after TMS, as well as the peripheral silent period and F-wave amplitudes after electrical peripheral nerve stimulation. We found a significant reduction of intracortical facilitation, which correlated significantly with riluzole plasma levels. To a lesser extent, intracortical inhibition was enhanced on day 1, motor threshold was increased on day 8 and F-wave amplitudes were reduced. These changes did not correlate with riluzole plasma levels. We conclude that the main effect of riluzole in vivo is a reduction of intracortical facilitation, which is closely related to the drug's level in the plasma. The most probable mechanism involves an effect on glutamatergic synaptic transmission.

Adult↗

PubMed2000

Cutaneomotor integration in humans is somatotopically organized at various levels of the nervous system and is task dependent.

Integration of tactile afferent signals with motor commands is crucial for the performance of purposeful movements such as during manipulation of an object in the hand. To study the somatotopic organization of sensorimotor integration we applied electrical peripheral conditioning stimuli to a digit located near (homotopic stimulation) or distant from (heterotopic stimulation) relaxed or isometrically contracted intrinsic hand muscles at variable time intervals prior to transcranial magnetic stimulation (TMS). Cutaneous stimulation has previously been shown to modulate the amplitude of the motor evoked potential (MEP) and to shorten the duration of the silent period (SP) evoked by TMS. In relaxed target muscles the time-dependent modulation of TMS-evoked motor responses by homotopic conditioning stimulation differed from modulation by heterotopic stimulation. Similar differences in the modulation pattern evoked by homotopic and heterotopic conditioning stimulation were observed for two distinct target muscles of the hand (abductor digiti minimi, abductor pollicis brevis muscle). Differences in modulation were maximal when the conditioning stimulation was applied 25-30 ms and 150-200 ms prior to TMS. Comparison of the modulation of the amplitudes of MEPs evoked by transcranial electrical stimulation (TES) and the modulation of those evoked by TMS suggests that differences between homotopic and heterotopic stimulation originate subcortically at 25- to 30-ms and, at least partially, cortically at 150- to 200-ms interstimulus intervals. In isometrically contracted intrinsic hand muscles the degree to which the SP was shortened reflected the location and the timing of the conditioning stimulus. Shortening was maximal when the conditioning stimulus was applied nearest to the contracted target muscle and 20 ms prior to the test stimulus. In contrast to the SP duration, the MEP size in voluntarily contracted target muscles was unaffected by the location of the conditioning stimulus. The somatotopic gradient of SP shortening was abolished when the two target muscles were simultaneously activated isometrically. Together, our findings suggest that somatotopy of input-output relationships is implemented at both a spinal and a cortical level in the human central nervous system and may also depend on the motor task involved.

Adult↗

PubMed2000

Motor cortex excitability in patients with cerebellar degeneration.

OBJECTIVES: To study motor cortex (M1) excitability and the effect of subthreshold transcranial magnetic stimulation (TMS) in patients with cerebellar degeneration and normals performing a reaction time (RT) task. METHODS: Time to wrist flexion after a visual go-signal was measured. TMS was always delivered at 90% of resting motor evoked potential (MEP) threshold. In one experiment, test TMS was delivered at various intervals after the go-signal. In half the trials priming TMS was also given with the go-signal. A second experiment examined the effect on RT of M1 and occipital priming stimulation alone. RESULTS: M1 excitability, measured as the likelihood of producing MEPs in the wrist flexor muscles, increased immediately after the go-signal in the patients and stayed high until movement. In controls, excitability rose gradually. This difference was largely eliminated by priming TMS. RT was longer in the patient group, but improved with priming TMS. Occipital priming produced less effect on RT than M1 stimulation in both controls (P=0.008) and patients (P=0.0004). CONCLUSIONS: M1 excitability prior to movement in an RT task increases abnormally early in cerebellar patients. This may reflect compensation for deficient thalamocortical drive. Subthreshold TMS can partially normalize the prolonged RT and abnormal excitability rise in cerebellar patients.

Adult↗

PubMed2000

Motor cortex disinhibition in acute stroke.

OBJECTIVES: To test whether a disinhibition occurs in the human motor cortex after stroke. METHODS: Patients with a mild to moderate hemiparesis after an acute unilateral ischemic stroke were compared with age-matched healthy controls. We used paired transcranial magnetic stimuli (TMS) to investigate intracortical inhibition and facilitation. Single TMS were applied to obtain a cortical silent period. RESULTS: Intracortical inhibition was significantly reduced in the affected hemisphere at interstimulus intervals of 2, 3 and 4 ms. The cortical silent period was significantly prolonged when compared to the unaffected hemisphere of the patients and to the control group. Motor cortex disinhibition observed in stroke patients was associated either with minimal impairment at the onset of symptoms or with rapidly improving motor functions. CONCLUSIONS: Motor cortex disinhibition occurs in humans after stroke. We suggest that this disinhibition is indicative of compensatory mechanisms, which are involved in recovery-related reorganization.

Acute Disease↗

PubMed2000

Training-induced changes of motor cortex representations in stroke patients.

OBJECTIVE: To study changes in motor cortex representations after a single session of physiotherapy in stroke patients. METHODS: TMS mapping was used to evaluate the motor output map of the abductor pollicis brevis (APB) in both hemispheres. Stroke patients (4-8 weeks after the infarction) were studied prior to a training session aimed at improving dexterity and 1 h and 1 day after the training. RESULTS: Prior to the training, the APB representation area in the affected hemisphere was significantly smaller than on the non-affected side. After therapy, the cortical motor output to the paretic APB was significantly enlarged, and motor function was improved. One day later, these effects were partially reversed. Motor thresholds remained significantly increased in the affected hemisphere before and after the therapy. CONCLUSION: A single session of physiotherapy produces a use-dependent enlargement of motor cortex representations paralleled by an improvement of motor function in stroke patients.

Adult↗

PubMed2000

Treatment-induced cortical reorganization after stroke in humans.

BACKGROUND AND PURPOSE: Injury-induced cortical reorganization is a widely recognized phenomenon. In contrast, there is almost no information on treatment-induced plastic changes in the human brain. The aim of the present study was to evaluate reorganization in the motor cortex of stroke patients that was induced with an efficacious rehabilitation treatment. METHODS: We used focal transcranial magnetic stimulation to map the cortical motor output area of a hand muscle on both sides in 13 stroke patients in the chronic stage of their illness before and after a 12-day-period of constraint-induced movement therapy. RESULTS: Before treatment, the cortical representation area of the affected hand muscle was significantly smaller than the contralateral side. After treatment, the muscle output area size in the affected hemisphere was significantly enlarged, corresponding to a greatly improved motor performance of the paretic limb. Shifts of the center of the output map in the affected hemisphere suggested the recruitment of adjacent brain areas. In follow-up examinations up to 6 months after treatment, motor performance remained at a high level, whereas the cortical area sizes in the 2 hemispheres became almost identical, representing a return of the balance of excitability between the 2 hemispheres toward a normal condition. CONCLUSIONS: This is the first demonstration in humans of a long-term alteration in brain function associated with a therapy-induced improvement in the rehabilitation of movement after neurological injury.

Adult↗

PubMed1999

Plasticity of cortical hand muscle representation in patients with hemifacial spasm.

To investigate interactions between face and hand representations in the human motor cortex, we studied patients with a hemifacial spasm before and after treatment with Botulinum toxin. Focal transcranial magnetic stimulation was used to assess the cortical motor output map of the abductor pollicis brevis muscle (APB) on both sides. Prior to therapy the representation of the APB ipsilateral to the facial muscle contractions (iAPB) was significantly smaller than on the contralateral side. Two weeks after successful therapy, the iAPB output area was significantly enlarged and expanded into the direction of the face representation. The results indicate activity dependent interactions between hand and face representations in the adult human motor cortex.

Adult↗

PubMed1999

Abnormal motor cortex organization contralateral to early upper limb amputation in humans.

We performed both a functional magnetic resonance imaging (fMRI) study using single slice FLASH technique and an investigation with transcranial magnetic stimulation (TMS) in a 21-year-old patient. He had suffered a left upper extremity amputation at age 7. Anteflexion of the amputation stump produced an unusual, broad activation contralateral to the movement. TMS revealed an enlarged cortical motor output area of the deltoid muscle at the amputation stump. Application of paired magnetic stimulation demonstrated decreased intracortical inhibition (ICI). A T1-weighted image indicated a lack of the characteristic shape of the central sulcus contralateral to the amputation. In addition to previous functional studies, these new structural data suggest that maturation of the central sulcus develops in response to daily practice of the contralateral hand, possibly until adolescence.

Adult↗

PubMed1999

Motor plasticity induced by synchronized thumb and foot movements.

We used focal transcranial magnetic stimulation to examine the effects of 120 synchronized thumb and foot movements on the motor output map of the right abductor pollicis brevis muscle (APB) (experiment 1). To evaluate the performance, the latencies between the onset of the electromyographic activity (EMG) of the two muscles were measured. As control, 120 asynchronous thumb and foot movements were performed (experiment 2). Exclusively in experiment 1, the center of gravity (CoG) of the output map moved medially in the direction of the foot representation area (mean 7 mm, P<0.05) and returned into its original location within 1 h. In experiment 2, the CoG remained unchanged (mean displacement, 0.68 mm into a lateral direction; not significant). The effect in experiment 1 was independent of an improvement in performance. We conclude that a short-lasting training of synchronous movements induces modulations of motor output maps which probably occur due to interactions between hand and foot representation areas in the motor cortex.

Adult↗

PubMed1999

Mapping plastic brain changes after acute lesions.

The combination of different mapping techniques has yielded new insights in reorganization processes after acute lesions in humans. Recent research focused not only on lesion-induced plasticity, but also on therapy-induced reorganization of the brain. Data from animal experiments has expanded our knowledge of mechanisms that underlie plastic changes.

Acute Disease↗

PubMed1999