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B Boroojerdi

Publications and source records attributed to B Boroojerdi.

33 records · Page 2Linked to original sources
PubMed2000

Reproducibility of intracortical inhibition and facilitation using the paired-pulse paradigm.

We have evaluated the reproducibility of intracortical inhibition (ICI) and facilitation (ICF) studied with paired-pulse focal transcranial magnetic stimulation. Three investigators studied the same subjects (n = 4) in three different sessions. A high variability was shown across subjects [coefficient of variation, (cv) 67.3% for ICI and 21.2% for ICF]. Intersession variability was up to 37.1% for ICI and 22.7% for ICF. Interinvestigator variability was 17.3% for ICI and negligible for ICF. Our results may have implications for planning future studies.

Adult↗
PubMed2000

Voluntary teeth clenching facilitates human motor system excitability.

OBJECTIVE: Voluntary contraction of the teeth is a common maneuver used to facilitate peripheral monosynaptic reflexes. It was the aim of this study to determine the site along the neuraxis where this effect occurs. METHODS: Focal transcranial magnetic stimulation (TMS) was used to measure recruitment curves, motor thresholds and intracortical inhibition and facilitation from the right first dorsal interosseus (FDI) and tibialis anterior (TA) muscles in seven normal volunteers. Changes in excitability in subcortical structures during teeth clenching were studied using F waves, H reflexes, and brainstem magnetic stimulation. RESULTS: Recruitment curves of FDI and TA showed significant facilitation during voluntary teeth clenching indicating an overall enhancement in the motor system excitability. Teeth clenching additionally resulted in decreased intracortical inhibition in the FDI but not in TA, pointing to an intracortical site of enhancement for the hand. Motor evoked potentials (MEPs) following stimulation at the brainstem level and F waves in FDI and soleus H reflex amplitude were also facilitated by teeth clenching, indicating a subcortical site for this effect for the upper and lower extremity. M wave amplitudes did not change. CONCLUSIONS: The teeth clenching maneuver had a similar facilitatory effect on upper and lower extremities. Cortical and subcortical sites contribute to this effect in a hand muscle while only subcortical sites were identified in this facilitatory effect on the lower extremity.

Adult↗
PubMed2000

Effects of low-frequency transcranial magnetic stimulation on motor excitability and basic motor behavior.

OBJECTIVE: To explore effects of low-frequency repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex (M1) on motor excitability and basic motor behavior in humans. DESIGN AND METHODS: Seven normal volunteers underwent 1 Hz rTMS of the hand representation of the right M1 for 15 min at an intensity of 115% of the individual resting motor threshold. The effects of rTMS on motor excitability were assessed by monitoring changes in individual resting motor threshold and input-output curves of motor evoked potentials (MEPs) in the flexor pollicis brevis, first dorsal interosseus, abductor digiti minimi and biceps brachii muscles. Changes in basic motor behavior were studied by measuring maximal and mean peak force and peak accelerations of thumb flexions and abductions of the fifth finger before and after rTMS. RESULTS: rTMS produced a significant increase in resting motor threshold and a significant suppression of MEP input-output curves that persisted for 30 min. The suppressing effect was restricted to the hand motor representation which was the prime target of the stimulation procedure, and there were no significant effects on the biceps representation. Peak force and peak acceleration were not affected while the motor representations of muscles involved in the behavioral measurements were significantly suppressed by rTMS. CONCLUSIONS: Low-frequency rTMS of M1 transiently depresses motor excitability but this does not affect basic motor behavior. This is relevant for the therapeutic use of low-frequency rTMS in disorders with abnormal cortical excitability.

Adult↗
PubMed2000

Changes in motor cortex excitability during ipsilateral hand muscle activation in humans.

OBJECTIVES: To test whether unilateral hand muscle activation involves changes in ipsilateral primary motor cortex (M1) excitability. METHODS: Single- and paired-pulse transcranial magnetic stimulation (TMS) of the right hemisphere was used to evoke motor evoked potentials (MEPs) from the resting left abductor pollicis brevis (APB) in 9 normal volunteers. We monitored changes in motor threshold (MT), MEP recruitment, intracortical inhibition (ICI) and intracortical facilitation (ICF) while the ipsilateral right APB was either at rest or voluntarily activated. Spinal motoneuron excitability was assessed using F-wave recording procedures. RESULTS: Voluntary muscle activation of the ipsilateral APB significantly facilitated the MEPs and F-waves recorded from the contralateral APB. Facilitation was observed with muscle activation >50% of the maximum voluntary force and with stimulus intensities >20% above the individual resting motor threshold. Intracortical inhibition significantly decreased in the ipsilateral M , while there was no significant change in intracortical facilitation during this maneuver. CONCLUSIONS: Unilateral hand muscle activation changes the excitability of homotopic hand muscle representations in both the ipsilateral M1 and the contralateral spinal cord. While the large proportion of MEP facilitation most likely occurred at a spinal level, involvement of the ipsilateral hemisphere may have contributed to the enlargement of magnetic responses.

Adult↗
PubMed2000

Enhanced excitability of the human visual cortex induced by short-term light deprivation.

Long-term deprivation of visual input for several days or weeks leads to marked changes in the excitability and function of the occipital cortex. The time course of these changes is poorly understood. In this study, we addressed the question whether a short period of light deprivation (minutes to a few hours) can elicit such changes in humans. Noninvasive transcranial magnetic stimulation (TMS) of the human occipital cortex can evoke the perception of flashes or spots of light (phosphenes). To assess changes in visual cortex excitability following light deprivation, we measured the minimum intensity of stimulation required to elicit phosphenes (phosphene threshold) and the number of phosphenes elicited by different TMS stimulus intensities (stimulus-response curves). A reduced phosphene threshold was detected 45 min after the onset of light deprivation and persisted for the entire deprivation period (180 min). Following re-exposure to light, phosphene thresholds returned to predeprivation values over 120 min. Stimulus-response curves were significantly enhanced in association with this intervention. In a second experiment, we studied the effects of light deprivation on functional magnetic resonance imaging (fMRI) signals elicited by photic stimulation. fMRI results showed increased visual cortex activation after 60 min of light deprivation that persisted following 30 min of re-exposure to light. Our results demonstrated a substantial increase in visual cortex excitability. These changes may underlie behavioral gains reported in humans and animals associated with light deprivation.

Adult↗
PubMed1999

Facilitation of picture naming after repetitive transcranial magnetic stimulation.

OBJECTIVE: To investigate the effect of repetitive transcranial magnetic stimulation (rTMS) on picture naming. BACKGROUND: Previous studies have shown that rTMS disrupts ongoing speech processes when delivered over frontal or parietal areas of the dominant hemisphere. METHODS: In 15 healthy right-handed male individuals, rTMS trains of 20 Hz with a duration of 2 seconds and an intensity of 55% of maximum stimulator output were delivered either to Wernicke's area, to the right-hemisphere homologue of Wernicke's area, to Broca's area, or to the primary visual cortex. Twenty black-and-white line drawings, which the individuals had to name as quickly as possible, were shown immediately after the completion of rTMS and again 2 minutes later. RESULTS: Immediately after the end of a train over Wernicke's area a shortening of naming latency was observed compared with naming without rTMS (p < 0.001). No significant effects on picture naming were observed 2 minutes later or at any time after stimulation of the right-hemisphere homologues of Wernicke's area, Broca's area, or the visual cortex. CONCLUSION: Repetitive transcranial magnetic stimulation over Wernicke's area leads to a brief facilitation of picture naming by shortening linguistic processing time.

Adult↗
PubMed1999

X-linked dominant Charcot-Marie-Tooth neuropathy: clinical, electrophysiological, and morphological phenotype in four families with different connexin32 mutations(1).

The sensorimotor neuropathy of the Charcot-Marie-Tooth type (CMT) is the most common hereditary disorder of the peripheral nervous system. The X-linked dominant form of CMT (CMTX) is associated with mutations in the gene for the gap junction protein connexin32. We examined four CMTX pedigrees two of which had potentially novel mutations in the only coding exon of connexin32. One previously unreported missense mutation, Ala39Val, was found in a family displaying a CMT phenotype with additional upper limb postural tremor reminiscent of a Roussy-Lévy syndrome. A novel single base insertion, 679insT, is among the first mutations found in the fourth transmembrane domain of connexin32. Frameshift and premature stop of translation are supposed to result in a non-functional carboxy-terminus. Two further families had the known missense mutations Arg15Trp and Arg22Gln. Several female carriers were found normal on clinical presentation, however, the genotype was paralleled by decreased nerve conduction velocities (NCV) and slowed central conduction of brain stem auditory evoked responses (BAER). Median motor NCVs showed mild (in women) to intermediate (in males) reduction, indicating a peripheral neuropathy with a predominating axonal component. Nerve biopsy findings were consistent with the electrophysiological data showing a marked loss of large myelinated fibres and clusters of regenerating axons. Electron microscopy revealed various alterations of the axoglial attachment zone. This suggests defective axon-Schwann cell interactions which may induce the axonopathy in CMTX.

Adolescent↗
PubMed1999

Localization of the motor hand area using transcranial magnetic stimulation and functional magnetic resonance imaging.

OBJECTIVE: The anatomical location of the motor area of the hand may be revealed using functional magnetic resonance imaging (fMRI). The motor cortex representation of the intrinsic hand muscles consists of a knob-like structure. This is omega- or epsilon-shaped in the axial plane and hook-shaped in the sagittal plane. As this knob lies on the surface of the brain, it can be stimulated non-invasively by transcranial magnetic stimulation (TMS). It was the aim of our study to identify the hand knob using fMRI and to reveal if the anatomical hand knob corresponds to the hand area of the motor cortex, as identified by TMS, by means of a frameless MRI-based neuronavigation system. METHODS: Suprathreshold transcranial magnetic stimuli were applied over a grid on the left side of the scalp of 4 healthy volunteers. The motor evoked potentials (MEPs) were recorded from the contralateral small hand muscles, and the centers of gravity (CoG) of the MEPs were calculated. The exact anatomical localization of each point on the grid was determined using a frameless MRI-based neuronavigation system. In each subject, the hand area of the motor cortex was visualized using fMRI during sensorimotor activation achieved by clenching the right hand. RESULTS: In all 4 subjects, the activated precentral site in the fMRI and the CoG of the MEP of all investigated muscles lay within the predicted anatomical area, the so-called hand knob. This knob had the form of an omega in two subjects and an epsilon in the other two subjects. CONCLUSIONS: TMS is a reliable method for mapping the motor cortex. The CoG calculated from the motor output maps may be used as an accurate estimation of the location of the represented muscle in the motor cortex.

Adult↗
PubMed1999

Evidence for a non-orthostatic origin of orthostatic tremor.

OBJECTIVES: Orthostatic tremor was first described by Heilman in 1984. It usually occurs in the legs during stance and decreases markedly during sitting or walking. The aim of this study was to determine if orthostatic tremor is invariably associated with the orthostatic and weight bearing conditions in the arms and legs, and to investigate the features of orthostatic tremor under different levels of peripheral loading. METHODS: Multichannel surface EMG recordings were obtained under different conditions (body posture and peripheral loading) from the proximal arm and leg muscles of seven patients fulfilling the clinical and electrophysiological criteria of orthostatic tremor. RESULTS: In weight bearing positions (stance; weight bearing on the hands on all fours), all patients showed 13 Hz-16 Hz tremor activity, predominantly in the active limb. No tremor activity could be found in a supine position with muscles at rest. Isometric contraction of the limbs in the supine position led to synchronous 13 Hz-16 Hz rhythmic activity in five patients. No tremor was seen when the subjects were suspended in a harness with relaxed legs. Isometric contraction of the legs in this position produced tremor in two patients. A stepwise reduction of the body weight by a harness reduced the tremor activity. Additional loading (10 kg-20 kg) during stance led to an increase in tremor amplitude, but tremor frequency remained unchanged. CONCLUSIONS: Orthostatic tremor is invariably present during stance or other weight bearing positions. It is not, however, always associated with orthostasis. In at least some patients it can be classified as an orthostasis independent action tremor. The failure of peripheral loading to modify tremor frequency indicates that orthostatic tremor may have a central, rather than a peripheral, origin.

Aged↗
PubMed1999

Transcallosal inhibition and motor conduction studies in patients with schizophrenia using transcranial magnetic stimulation.

BACKGROUND: Transcranial magnetic stimulation of the motor cortex may not only elicit excitatory responses in hand muscles contralateral to the stimulated hemisphere, but may also suppress tonic voluntary electromyogram activity in muscles ipsilateral to the stimulation. This inhibition is mediated between the motor cortices via the corpus callosum. AIMS: To investigate motor excitability and interhemispheric (transcallosal) connections in patients with schizophrenia. METHOD: Transcallosal inhibition and motor conduction parameters were investigated in ten patients with schizophrenia and in ten age- and gender-matched healthy subjects. RESULTS: Transcallosal conduction time (TCT) and duration of the inhibition were significantly longer in patients with schizophrenia (mean (s.d.)): TCT, 12.4 (2.9) ms in normal subjects and 15.3 (2.6) ms in patients (P = 0.03); mean duration, 34.1 (4.9) ms in normal subjects and 51.9 (16.8) ms in patients (P = 0.01). CONCLUSIONS: Magnetic motor conduction parameters are unaltered in schizophrenia, but transcallosal inhibition is significantly delayed and prolonged. This may indicate abnormal function of the corpus callosum in these patients.

Adult↗
PubMed1998

[Subacute encephalopathy with epileptic seizures in a patient with chronic alcoholism (SESA syndrome)].

Subacute encephalopathy with seizures in alcoholics (SESA syndrome) is a rare disease entity following chronic alcohol ingestion. It is quite distinct from alcohol withdrawal syndromes, such as delirium, withdrawal seizures or CNS complications of alcohol, such as Wernicke-Korsakow syndrome, central pontine myelinolysis or Marchiafava-Bignami disease, and was proposed in 1981 by Niedermeyer and coworkers. This syndrome consists of multiple neurological deficits, such as hemiparesis or hemianopia, and of recurrent focal and generalized seizures associated with prominent EEG features (periodic lateralized discharges, PLEDs). A 72-year-old Caucasian male with chronic alcoholism and an otherwise unremarkable past medical history was admitted to our hospital because of several secondary generalized simple partial seizures. Laboratory investigations revealed elevated levels of gamma-glutamyltranspeptidase and of mean corpuscular volume. Other laboratory investigations and the CSF examinations on three occasions revealed normal values. Cranial computed and magnetic resonance tomography showed cerebral microangiopathy and generalized atrophy. Despite triple anticonvulsive therapy and an intravenous treatment with acyclovir and thiamine, the epileptic seizures persisted. Several EEGs revealed left parietooccipital periodic lateralized epileptiform discharges (PLEDs). The patient died of an intercurrent pulmonary infection about 3 months after the onset of symptoms. The described clinical picture resembles the symptoms of SESA syndrome.

Aged↗
PubMed1998

Interhemispheric inhibition in patients with multiple sclerosis.

OBJECTIVES: A single focal magnetic stimulus applied to the motor cortex of normal subjects can suppress ongoing voluntary electromyographic activity in ipsilateral small hand muscles. This inhibition is mediated from one motor cortex to the contralateral side via a transcallosal pathway. METHODS: We have investigated transcallosal inhibition in 24 patients with definite multiple sclerosis (MS) and in 24 healthy volunteers. A focal magnetic stimulus was applied to the hand area of the motor cortex and the onset latency of the inhibition of the ongoing EMG activity of the ipsilateral first dorsal interosseus muscle was evaluated. Cortico-motor conduction time to the same muscle was revealed, using a magnetic stimulus over the contralateral motor cortex. The difference between these values was calculated as transcallosal conduction time. Cerebral magnetic resonance imaging (MRI) scans including sagittal T2-weighted images were performed in 18 patients. RESULTS: The depth of inhibition (maximal inhibition as percentage of the baseline EMG) in the MS patients was comparable to normal values, but the transcallosal conduction time was significantly delayed (patients 17.2 +/- 6.4 ms; normal subjects 12.2 +/- 2.6 ms; P < 0.001). The duration of the inhibition was significantly prolonged in MS patients (patients 47.9 +/- 20.9 ms; normal subjects 38.9 +/- 10.1 ms; P = 0.02). Transcallosal conduction time was delayed in 11 (46%) of 24 patients, compared with normal subjects. It exceeded the normal range (mean +/- 2.5 SD) in one normal subject (specificity 96%). No correlation could be found between the size or extent of the lesions obtained from the MRI scan and the onset latency or the depth of the inhibition. CONCLUSIONS: We conclude that conduction over transcallosal connections is significantly slower in patients with MS.

Adult↗
PubMed1998

Botulinum toxin treatment of synkinesia and hyperlacrimation after facial palsy.

OBJECTIVES: To investigate the effects of injection of botulinum toxin type A (BTX A) into the orbicularis oculi muscle and lacrimal gland in patients with aberrant regeneration after facial palsy (facial synkinesias and hyperlacrimation). METHODS: The effect of the toxin injection (on average 75 mouse units of BTX A) into the orbicularis oculi muscle on facial synkinesias was assessed on a five point (0 to 4) scale in 10 patients with aberrant regeneration of facial nerve fibres after a peripheral facial nerve palsy. Six patients underwent a videographic control, which was assessed by a blinded independent investigator. In two patients with hyperlacrimation an extra dose of botulinum toxin (on average 20 mouse units BTX A) was injected into the lacrimal gland and the effect was assessed using the Schirmer test and on a three point scale. RESULTS: Botulinum toxin type A had a good to excellent (grades 3 and 4) effect over an average of six months after 91% of injections. In 9% the injections had a moderate (grade 2) effect. Patients with hyperlacrimation showed a nearly complete recovery. There were no systemic side effects but focal side effects due to a temporary weakness of the orbicularis oculi muscle were not uncommon. CONCLUSIONS: Botulinum toxin type A is the treatment of choice in motor and autonomic effects of aberrant regeneration of facial nerve after a peripheral palsy. The required dose is similar to or slightly lower than the dose usually recommended for hemifacial spasm.

Adult↗
PubMed1996

Transcallosal inhibition in cortical and subcortical cerebral vascular lesions.

The excitability of the motor cortex after transcranial magnetic stimulation was investigated in 10 patients with purely subcortical, and in 22 patients with cortical-subcortical cerebrovascular lesions. In the first investigation we applied magnetic double stimuli over both motor cortices with different inter-stimulus intervals. The first (conditioning) stimulus was applied to the affected hemisphere and the second stimulus (test stimulus) to the unaffected side. The responses of the first dorsal interosseal (FDI) muscle, contralateral to the test stimulus, were recorded after applying the test stimulus alone and at inter-stimulus intervals of 5 ms, 7 ms, 15 ms, 30 ms and 60 ms. In a second investigation the patients were asked to activate their non-paretic first dorsal interosseus muscle and the magnetic stimulus was applied over the affected hemisphere. The EMG responses were rectified and averaged. Patients with subcortical cerebral lesions below the centrum semiovale (i.e., having no effect on the transcallosal fibres) displayed a pronounced inhibition of one motor cortex after the stimulation of the contralateral side, comparable with normal subjects. Patients with cortical-subcortical cerebral lesions displayed only partly less inhibition of their motor cortex but the results in this group were not uniform. Since inhibition was preserved in patients with subcortical lesions, which had destroyed the corticospinal tract, we conclude that this inhibition is not mediated through an ipsilateral projection but via a transcallosal route.

Adult↗