Biomedical subjects

Babak Boroojerdi

Publications and source records attributed to Babak Boroojerdi.

8 recordsLinked to original sources

PubMed2003

Motor cortex hand area and speech: implications for the development of language.

Recently a growing body of evidence has suggested that a functional link exists between the hand motor area of the language dominant hemisphere and the regions subserving language processing. We examined the excitability of the hand motor area and the leg motor area during reading aloud and during non-verbal oral movements using transcranial magnetic stimulation (TMS). During reading aloud, but not before or afterwards, excitability was increased in the hand motor area of the dominant hemisphere. This reading effect was found to be independent of the duration of speech. No such effect could be found in the contralateral hemisphere. The excitability of the leg area of the motor cortex remained unchanged during reading aloud. The excitability during non-verbal oral movements was slightly increased in both hemispheres. Our results are consistent with previous findings and may indicate a specific functional connection between the hand motor area and the cortical language network.

Adult↗

PubMed2003

Power grip disinhibits the ipsilateral sensorimotor cortex: a TMS and fMRI study.

Electrophysiological studies have shown that forceful activation of the hand muscles (power grip) is accompanied by an increased excitability of the ipsilateral corticospinal system. This increase in excitability may be due to spinal or cortical mechanisms. Here we show with fMRI that this phenomenon is at least in part mediated at a cortical level. We used TMS to show that the increased ipsilateral excitability during a forceful maneuver leads to enhanced stimulus-response curves. fMRI was used to compare the activation during a repetitive hand movement with or without an accompanying power grip on the opposite site. The power grip reduced movement-related activation in the ipsilateral sensorimotor cortex. Peak deactivation was located in the left postcentral gyrus extending into the adjacent precentral gyrus. This finding suggests that a forceful activation of the hand muscles disinhibits a distinct functional representation in the ipsilateral sensorimotor cortex. Consequently, the excitability of the corticospinal system increases and less neuronal excitatory activity is needed to perform a given task. The results may be important for a variety of studies as they suggest that fMRI may show decreased hemodynamic response under conditions in which other neurophysiological methods have shown increased functional activity.

Brain Mapping↗

PubMed2003

Repetitive transcranial magnetic stimulation of the parietal cortex transiently ameliorates phantom limb pain-like syndrome.

OBJECTIVE: Phantom pain is linked to a reorganization of the partially deafferented sensory cortex. In this study we have investigated whether the pain syndrome can be influenced by repetitive transcranial magnetic stimulation (rTMS). METHODS: Two patients with a longstanding unilateral avulsion of the lower cervical roots and chronic pain in the arm were studied. As a control the acute effects of rTMS (15 Hz, 2 s duration) on pain were studied in 4 healthy subjects. Pain intensity was assessed with the Visual Analogue Scale. RESULTS: Stimulation of the contralateral parietal cortex led to a reproducible reduction in pain intensity lasting up to 10 min. Stimulation of other cortical areas produced only minor alterations in the severity of the pain. Both 1 and 10 Hz rTMS trains applied to the contralateral parietal cortex on weekdays for 3 consecutive weeks did, however, not lead to permanent changes in the pain intensity. Experimentally induced pain (cold water immersion of the right hand) in normal subjects was not influenced by rTMS. CONCLUSIONS: These results do not favor the use of rTMS in the treatment of phantom limb pain. The results, however, support the concept that phantom pain is due to a dysfunctional activity in the parietal cortex. The transient rTMS-induced analgesic effect may be due to a temporary interference with the cerebral representation of the deafferented limb.

Adult↗

PubMed2002

Early consolidation in human primary motor cortex.

Behavioural studies indicate that a newly acquired motor skill is rapidly consolidated from an initially unstable state to a more stable state, whereas neuroimaging studies demonstrate that the brain engages new regions for performance of the task as a result of this consolidation. However, it is not known where a new skill is retained and processed before it is firmly consolidated. Some early aspects of motor skill acquisition involve the primary motor cortex (M1), but the nature of that involvement is unclear. We tested the possibility that the human M1 is essential to early motor consolidation. We monitored changes in elementary motor behaviour while subjects practised fast finger movements that rapidly improved in movement acceleration and muscle force generation. Here we show that low-frequency, repetitive transcranial magnetic stimulation of M1 but not other brain areas specifically disrupted the retention of the behavioural improvement, but did not affect basal motor behaviour, task performance, motor learning by subsequent practice, or recall of the newly acquired motor skill. These findings indicate that the human M1 is specifically engaged during the early stage of motor consolidation.

Adult↗

PubMed2002

Improving hand function in chronic stroke.

BACKGROUND: Recovery of function following stroke plateaus in about 1 year, typically leaving upper arm function better than that in the hand. Since there is competition among body parts for territory in the sensorimotor cortex, even limited activity of the upper arm might prevent the hand from gaining more control, particularly when the territory is reduced in size because of the stroke. Deafferentation of a body part in a healthy brain enhances cortical representations of adjacent body parts, and this effect is markedly increased by voluntary activity of the adjacent part. OBJECTIVE: To explore whether deafferentation of the upper arm, produced by a new technique of regional anesthesia during hand motor practice, helps recovery of hand function in patients with long-term stable weakness of their hand following stroke. METHODS AND RESULTS: Deafferentation, produced by a new technique of regional anesthesia of the upper arm during hand motor practice, dramatically improved hand motor function including some activities of daily living. The improvement was associated with an increase in transcranial magnetic stimulation-evoked motor output to the practice hand muscles. CONCLUSION: This is a novel therapeutic strategy that may help improve hand function in patients with long-term weakness after stroke.

Afferent Pathways↗

PubMed2002

Visual and motor cortex excitability: a transcranial magnetic stimulation study.

OBJECTIVES: Phosphene thresholds (PTs) to transcranial magnetic stimulation over the occipital cortex and motor thresholds (MTs) have been used increasingly as measures of the excitability of the visual and motor cortex. MT has been utilized as a guide to the excitability of other, non-motor cortical areas such as dorsolateral prefrontal cortex. The aims of this study were to compare the PTs to MTs; to assess their stability across sessions; and to investigate their relation to MTs. METHODS: PTs and MTs were determined using focal transcranial magnetic stimulation over the visual and motor cortex. RESULTS: PTs were shown to be significantly higher than MTs. Both PTs and MTs were stable across sessions. No correlation between PTs and MTs could be established. CONCLUSIONS: Phosphene threshold is a stable parameter of the visual cortex excitability. MTs were not related to the excitability of non-motor cortical areas.

Adult↗

PubMed2002

Cortical excitability changes induced by deafferentation of the contralateral hemisphere.

Short-term deprivation of sensory input by ischaemic nerve block (INB) leads to functional reorganization in the deafferented motor cortex. Here, we show that INB also elicits functional changes in homotopic regions of the cortex contralateral to the deafferented one. We measured motor evoked potential (MEP) amplitudes elicited by transcranial magnetic stimulation (TMS) in small hand and biceps brachii muscles before, during and after INB of the right hand. INB increased excitability of the cortical representation of (i) the intact hand and (ii) body parts proximal to the deafferented hand (upper arm), in the absence of excitability changes in other body part representations such as thorax or leg muscles. This effect persisted throughout the entire period of deafferentation and returned to baseline values afterward. Motor responses to brainstem electrical stimulation remained unchanged during INB, indicating that the effect is probably of cortical origin. Lorazepam, a GABA(A) receptor agonist, blocked this increased excitability. Interhemispheric inhibition between hand muscles decreased during INB. After chronic deafferentation in amputees, MEP amplitudes and motor output curves in small hand muscles were depressed and motor thresholds were elevated compared with aged-matched controls. These results indicate that acute hand deafferentation can elicit a focal increase in excitability in the hand motor representation contralateral to the deafferented cortex that is influenced by transcallosal interactions and GABAergic transmission, and is balanced in the setting of chronic deafferentation.

Adult↗

PubMed2002

Pharmacologic influences on TMS effects.

Transcranial magnetic stimulation (TMS) has been used increasingly to probe the physiology of the human cortex. Besides measuring directly the cortical excitability in motor and visual systems, this noninvasive method can be used to study short- and long-term cortical plasticity. One possible method to examine basic mechanisms underlying cortical excitability and plasticity in humans is the combination of TMS and pharmacologic interventions. In this review the author describes TMS paradigms used to study mechanisms of plasticity in the intact human motor system and its excitability using pharmacologic methods.

Electric Stimulation↗