Biomedical subjects

Lucy H A Strens

Publications and source records attributed to Lucy H A Strens.

6 recordsLinked to original sources

PubMed2004

Functional significance of the ipsilateral hemisphere during movement of the affected hand after stroke.

Previous fMRI observations have suggested increased task-related activation of the ipsilateral cerebral motor cortex in patients recovering from stroke. This is generally taken to infer an increased output from this area, although the functional relevance of this has been questioned. Here, we use directed EEG coherence to reveal whether there is increased informational flow from the ipsilateral motor cortex following motor stroke, and through correlation with degree of recovery, establish that this pattern of activity is associated with limited functional improvement. Unrecovered (n = 14), recovered (n = 11) patients and healthy subjects (n = 16) performed an isometric grip task with either hand that corresponded to 25% of individual maximum force, while EEG was recorded. For unrecovered stroke patients, most task-related information flow between the sensorimotor cortices in the low beta band of the EEG came from the ipsilateral (undamaged) hemisphere during grip with the affected hand. This was not the case when they gripped with their unaffected hand, when cortical activity was driven from the contralateral sensorimotor cortex. The latter pattern was also seen in recovered patients and controls. These findings suggest a functional role for the ipsilateral hemisphere in organizing movement of the impaired limb following stroke, but only in those patients that do not make a good functional recovery. Patients making a fuller recovery organize movement-related cortical activity from the hemisphere contralateral to movement.

Adolescent↗

PubMed2004

Misdiagnosing the vegetative state after severe brain injury: the influence of medication.

Patients who suffer severe brain damage may be left unaware of self and of the environment and in a permanent vegetative state (PVS). The difficulties in correctly ascertaining unawareness after brain injury have been emphasized by a number of authors. It is well recognized that toxic-metabolic and drug-induced cerebral depression occurs acutely after brain injury. However, less attention has been drawn to the effects of medication months after brain injury and the way in which medication may confound assessment of awareness and, thus, the reliable assessment of long-term prognosis. This paper describes two patients who sustained a severe and well-documented structural brain injury, one hypoxic and one traumatic. Both were unaware when first seen at 3 months post-injury, but both have made useful functional recovery. The paper discusses their progress and how the early prescription of large doses of anti-epileptic drugs, sedatives and anti-spastic agents in these circumstances may result in an initial misdiagnosis of the vegetative state.

Adolescent↗

PubMed2003

The ipsilateral human motor cortex can functionally compensate for acute contralateral motor cortex dysfunction.

What promotes motor recovery from stroke? To date, studies of recovery from stroke have shown alterations in function in various cortical areas, including the contralesional (unaffected) motor cortex (M1). However, whether these changes contribute to recovery or are mere epiphenomena remains unclear. We therefore sought evidence that the ipsilateral M1 can compensate for dysfunction of the contralateral M1. We recorded the change in force production during a finger-tapping task in response to acute disruption of M1 function by repetitive transcranial magnetic stimulation (rTMS). Neither control (occipital) nor ipsilateral M1 rTMS lead to a change in tapping force. RTMS over contralateral M1 had a short-lived effect and induced changes in ipsilateral M1 excitability around the time that these behavioral effects abated, consistent with delayed compensation by the ipsilateral M1. Simultaneous bilateral M1 stimulation, designed to prevent compensation by the ipsilateral M1, had a large and prolonged effect on tapping force. This is the first demonstration that the ipsilateral primary motor cortex is capable of functionally significant compensation for focal contralateral cortical dysfunction in the adult human and provides a rational basis for interventional treatments aimed at promoting functional compensation in unaffected cortical areas after stroke.

Biomechanical Phenomena↗

PubMed2002

Persistent effects of high frequency repetitive TMS on the coupling between motor areas in the human.

Repetitive transcranial magnetic stimulation (rTMS) shows promise as a treatment for various movement and psychiatric disorders. How rTMS may have persistent effects on cortical function remains unclear. We hypothesised that it may act by modulating cortico-cortical connectivity. To this end we assessed cortico-cortical coherence before and after high frequency rTMS of the motor cortex. Sixteen healthy subjects received a single train (5 Hz, active motor threshold, 50 stimuli) of rTMS to the left motor hand area. Spectral power and coherence estimates were calculated between different EEG signals at rest and while muscles of the distal upper limb were tonically contracted. Repetitive TMS over the left motor hand area caused a significant decrease in the intrahemispheric EEG-EEG coherence between motor and premotor cortex in the 10.7-13.6 Hz (upper alpha band) lasting a few minutes after stimulation. There was no significant change in interhemispheric EEG-EEG coherence between motor areas. Thus, high frequency rTMS of the motor cortex decreases ipsilateral cortico-cortical intrahemispheric in the upper alpha band.

Adult↗

PubMed2002

Repetitive transcranial magnetic stimulation of the supplementary motor area (SMA) degrades bimanual movement control in humans.

Moving the upper limbs at a common tempo according to an in-phase or anti-phase mode represents elementary coordination dynamics. Previously, the role of the supplementary motor area (SMA) has been emphasized for successful production of these patterns. The objective of this study was to investigate whether repetitive transcranial magnetic stimulation (rTMS) of the SMA at 5 Hz can interfere with these isofrequency configurations in the post-stimulation stage. Results showed a deterioration of temporal control as a function of coordinative complexity. This effect was associated with a decrease in the functional coupling between the primary motor cortices, as measured by electroencephalographic coherence. These data suggest that rTMS of the SMA can modify interhemispheric communication and accordingly modulate interlimb behavior.

Adult↗

PubMed2002

The effects of subthreshold 1 Hz repetitive TMS on cortico-cortical and interhemispheric coherence.

OBJECTIVES: Repetitive transcranial magnetic stimulation (rTMS) shows promise as a treatment for various movement and psychiatric disorders. Just how rTMS may have persistent effects on cortical function remains unclear. We hypothesised that it may act by modulating cortico-cortical and interhemispheric connectivity. To this end we assessed cortico-cortical and interhemispheric coherence before and after low frequency, subthreshold rTMS of the left motor cortex. METHODS: Fifteen healthy subjects received one train (1Hz, 90% of active motor threshold, 1500 stimuli) of rTMS to the left motor hand area. Spectral power and coherence estimates were calculated between different electroencephalogram (EEG) signals at rest and while muscles of the distal upper limb were tonically contracted. RESULTS: rTMS over the left motor hand area caused a significant increase in ipsilateral EEG-EEG coherence and in the interhemispheric coherence between motor areas in the alpha band. The effects of rTMS lasted up to 25 min post-stimulation. There was no significant change in EEG-EEG coherence over the hemisphere contralateral to stimulation. CONCLUSIONS: Low frequency, subthreshold rTMS of the motor cortex increases ipsilateral cortico-cortical and interhemispheric coherence in the alpha band. This may, in part, mediate the inhibitory effects of low frequency rTMS.

Adult↗