Biomedical subjects

Ying-Zu Huang

Publications and source records attributed to Ying-Zu Huang.

11 recordsLinked to original sources

PubMed2006

Effects of theta burst stimulation protocols on phosphene threshold.

OBJECTIVE: We investigated the effects on occipital cortex, of two newly developed methods of repetitive transcranial magnetic stimulation (rTMS): continuous and intermittent theta burst stimulation (cTBS and iTBS), that lead to long lasting changes in excitability when applied over primary motor cortex. METHODS: Phosphene threshold to a single TMS pulse was measured before and after application of either continuous or intermittent theta burst stimulation (cTBS/iTBS; 600 total pulses at 80% phosphene threshold). RESULTS: In our cohort, cTBS increased phosphene threshold by an average of 10%. In contrast, iTBS, which transiently increases motor cortex excitability, had no effect on phosphene threshold. CONCLUSIONS: cTBS can be applied successfully to non-motor areas of cortex, but iTBS may need modification to produce maximal effects. SIGNIFICANCE: cTBS maybe a new useful tool in disorders characterized by an abnormal state of activity of the visual cortex.

Adult↗

PubMed2006

Abnormalities in motor cortical plasticity differentiate manifesting and nonmanifesting DYT1 carriers.

A mutation in the DYT1 gene causes dominantly inherited childhood-onset primary dystonia, but intriguingly, only 30 to 40% of those who carry the mutation ever develop symptoms. We have used the unique model provided by this group of patients to investigate the hypothesis that abnormalities in brain plasticity underlie the pathophysiology of primary dystonia. We recruited 8 DYT1 gene carriers with dystonia, 6 DYT1 gene carriers without dystonia, 6 patients with sporadic primary dystonia (torticollis), and 10 healthy control subjects. Groups were age-matched. We compared the effect in these groups of subjects of repetitive transcranial magnetic stimulation (rTMS) delivered to the motor cortex, by assessing changes in corticospinal excitability following rTMS. rTMS was given in the form of theta burst stimulation (TBS) using the inhibitory protocol "cTBS" (total of 300 pulses in 50-Hz bursts given every 5Hz). DYT1 gene carriers with dystonia and subjects with torticollis had a significantly prolonged response to rTMS in comparison with healthy subjects. In contrast, DYT1 gene carriers without dystonia had no significant response to rTMS. These data demonstrate an excessive response to an experimental "plasticity probing protocol" in subjects with dystonia, but a lack of response in genetically susceptible individuals who have not developed dystonia. These preliminary data suggest that the propensity to undergo plastic change may affect the development of symptoms in genetically susceptible individuals and that this may be an important mechanism in the pathogenesis of primary dystonia in general.

Adult↗

PubMed2005

The role of dorsal premotor area in reaction task: comparing the "virtual lesion" effect of paired pulse or theta burst transcranial magnetic stimulation.

We compared the effect on reaction times of transient interference with function of the dorsal premotor cortex (PMd) using a pair (25-ms interval) of transcranial magnetic stimulation (TMS) pulses with long-term interference produced by a new repetitive TMS paradigm known as "theta burst stimulation" (TBS). Pairs of TMS pulses over left PMd increased choice but not simple reaction times of the right hand if given at the onset of the reaction interval. There was no effect of stimulation over right PMd or at a midline parietal control site (Pz). In contrast, TBS over either left or right PMd increased choice RTs of both hands for at least 5-10 min after the end of TBS. Pairs of TMS pulses over left PMd also increased error rates whereas TBS had no effect on error rates despite the effect on RTs. We suggest that TBS leads to widespread changes in activity and more complex effects on behaviour than expected from the paired pulse TMS and conclude that transient and long-term forms of interference with function may influence behavioural tasks in subtly different ways.

Adult↗

PubMed2005

Theta burst stimulation of the human motor cortex.

It has been 30 years since the discovery that repeated electrical stimulation of neural pathways can lead to long-term potentiation in hippocampal slices. With its relevance to processes such as learning and memory, the technique has produced a vast literature on mechanisms of synaptic plasticity in animal models. To date, the most promising method for transferring these methods to humans is repetitive transcranial magnetic stimulation (rTMS), a noninvasive method of stimulating neural pathways in the brain of conscious subjects through the intact scalp. However, effects on synaptic plasticity reported are often weak, highly variable between individuals, and rarely last longer than 30 min. Here we describe a very rapid method of conditioning the human motor cortex using rTMS that produces a controllable, consistent, long-lasting, and powerful effect on motor cortex physiology and behavior after an application period of only 20-190 s.

Adult↗

PubMed2005

High-frequency repetitive transcranial magnetic stimulation over the hand area of the primary motor cortex disturbs predictive grip force scaling.

When we repetitively lift an object, our grip force is influenced by the mechanical object properties of the preceding lift, irrespective of whether the subsequent lift is performed with the same hand or the hand opposite to the preceding lift. This study investigates if repetitive high-frequency transcranial magnetic stimulation (rTMS) over the dominant primary motor cortex affects this relationship. After completion of 10 lifts of an object using the dominant hand, rTMS was applied over the dominant primary motor cortex for 20 s. On the first lift following rTMS, the peak grip force was significantly higher than on the lift preceding rTMS. Moreover, this measure remained elevated throughout the following set of lifts after rTMS. rTMS did not change the peak lift force generated by more proximal arm muscles. The same effect was observed when the lifts following rTMS over the dominant motor cortex were performed with the ipsilateral hand. These effects were not observed when subjects rested both hands on their lap or when a sham stimulation was applied for the same period of time. These preliminary data suggest that rTMS over the sensorimotor cortex disturbs predictive grip force planning.

Adult↗

PubMed2004

Abnormal cortical and spinal inhibition in paroxysmal kinesigenic dyskinesia.

Paroxysmal kinesigenic dyskinesia (PKD) is characterized by brief episodes of choreic/dystonic movements precipitated by sudden movement. The condition responds to antiepileptic medication, particularly carbemazepine. Autosomal dominant inheritance is often seen, and a locus in the pericentromeric region of chromosome 16 has been identified in some families. Little is known of the pathophysiology of PKD, although an ion channel abnormality is thought likely. We assessed a number of electrophysiological parameters in 11 patients with idiopathic PKD, a proportion of them on and off treatment. We identified reduced short intracortical inhibition (SICI), reduced early phase of transcallosal inhibition, and a reduced first phase of spinal reciprocal inhibition (RI) in subjects with PKD. The cortical silent period, the startle response and the second and third phases of RI were normal. Treatment with carbamazepine normalized the abnormalities in transcallosal inhibition, but had no effect on other parameters. Patients with PKD show a discrete set of abnormalities in cortical and spinal inhibitory circuits that differ from those seen in primary dystonia and epilepsy, and which may provide clues to the underlying pathophysiology of the disorder.

Adolescent↗

PubMed2004

Interhemispheric interaction between human dorsal premotor and contralateral primary motor cortex.

We used transcranial magnetic stimulation (TMS) in a paired pulse protocol to investigate interhemispheric interactions between the right dorsal premotor (dPM) and left primary motor cortex (M1) using interstimulus intervals of 4, 6, 8, 10, 12, 16 and 20 ms in ten healthy subjects. A conditioning stimulus over right dPM at an intensity of either 90 or 110% resting motor threshold (RMT) suppressed motor-evoked potentials (MEPs) evoked in the first dorsal interosseous (FDI) muscle by stimulation of left M1. Maximum effects occurred for interstimulus intervals (ISIs) of 8-10 ms. There was no effect if the conditioning stimulus was applied 2.5 cm lateral, anterior or medial to dPM. The effect differed from previously described M1 interhemispheric inhibition in that the threshold for the latter was greater than 90% RMT, whereas stimulation of the dPM at the same intensity led to significant inhibition. In addition, voluntary contraction of the left FDI (i.e. contralateral to the conditioning TMS) enhanced interhemispheric inhibition from right M1 but had no effect on the inhibition from right dPM. Finally, conditioning to right dPM at 90% RMT reduced short-interval intracortical inhibition (SICI; at ISI = 2 ms) in left M1 whilst there was no effect if the conditioning stimulus was applied to right M1. We conclude that conditioning TMS over dPM has effects that differ from the previous pattern of interhemispheric inhibition described between bilateral M1s. This may reflect the existence of commissural fibres between dPM and contralateral M1 that may play a role in bimanual coordination.

Adult↗

PubMed2004

One-Hz repetitive transcranial magnetic stimulation of the premotor cortex alters reciprocal inhibition in DYT1 dystonia.

Repetitive transcranial magnetic stimulation (rTMS) can produce long-lasting effects not only underneath the site of stimulation, but also at distant connected sites. This study aimed to assess how low frequency rTMS over the premotor area might affect abnormalities in spinal motor function in patients with generalised dystonia associated with the DYT1 gene mutation. We assessed reciprocal inhibition (RI) in a group of 8 manifesting carriers of the DYT1 gene (DYT1) and 10 healthy controls. All subjects then received 20 minutes of 1 Hz rTMS over the premotor area, and RI was assessed again. Before rTMS, the second and third phases of RI were abnormal in DYT1 subjects compared to controls. After 20 minutes of 1 Hz rTMS over the premotor area, a significant increase in inhibition was noted in the third and possibly the first phase of RI in the DYT1 group. No changes in RI were observed in control subjects after rTMS. We have shown for the first time to date that reducing cortical excitability in patients with dystonia using rTMS can produce corresponding changes in abnormal spinal motor output. These findings make a case for further exploring rTMS as a tool to modulate abnormal cortical and spinal excitability in individuals with dystonia and even as a potential form of treatment for dystonic symptoms.

Adult↗

PubMed2004

The effect of short-duration bursts of high-frequency, low-intensity transcranial magnetic stimulation on the human motor cortex.

OBJECTIVE: To explore the effect of applying a short burst of high-frequency repetitive transcranial magnetic stimulation (rTMS) to the human motor cortex as a preparatory investigation before attempting theta burst stimulation in humans. METHODS: Five or 15 pulses of 50 Hz rTMS were given at 50-80% active motor threshold (AMT). The time course of changes in motor-evoked potential (MEP) size and short interval intracortical inhibition (SICI) were evaluated from 20 to 300 ms after the end of each burst in the relaxed first dorsal interosseous muscle of 15 healthy volunteers. RESULTS: No subjects noted any adverse effects. MEPs were enhanced and SICIs were reduced at 20 ms after a burst of either 5 or 15 pulses at 70 or 80% AMT, but not at 50% AMT. Subsequent experiments used a 5 pulse burst at 80% AMT. The threshold for producing SICI increased from 60 to 80% AMT when tested 10 or 20 ms after the end of the burst. MEPs were enhanced for 100 ms, whereas SICI was reduced for 200-300 ms. CONCLUSIONS: A short burst of low-intensity 50 Hz rTMS over the hand motor area transiently increases MEP amplitude with a longer lasting decrease in SICI. SIGNIFICANCE: This means that it may be possible in future experiments to apply theta burst conditioning safely to the human cortex.

Adult↗

PubMed2003

Different patterns of electrophysiological deficits in manifesting and non-manifesting carriers of the DYT1 gene mutation.

A mutation in the DYT1 gene on chromosome 9q34 causes early-onset primary torsion dystonia with autosomal dominant inheritance but low phenotypic penetrance. The aim of the present study was to assess the functional consequences of the DYT1 gene, by comparing the electrophysiology of cortical and spinal circuits in clinically affected and unaffected carriers of the DYT1 gene mutation. We assessed intracortical inhibition (ICI), intracortical facilitation (ICF), the cortical silent period (SP) and spinal reciprocal inhibition (RI) in 10 manifesting DYT1 gene carriers (MDYT1), seven non-manifesting DYT1 gene carriers (NMDYT1) and 13 healthy controls. The MDYT1 subjects had abnormalities similar to those seen in previous studies of non-genetically characterized individuals with primary dystonia. They had reduced ICI, shorter SP and absent presynaptic phase of RI compared with the healthy controls. NMDYT1 subjects also had a significant reduction in cortical inhibition (ICI and SP), but their spinal RI was not different from controls. We conclude that clinical expression of dystonia depends on widespread electrophysiological deficits, and the presence of the DYT1 gene mutation itself leads only to a subset of these changes. This is consistent with the hypothesis that additional environmental/genetic insults may be needed to reveal clinical symptoms in DYT1 gene carriers.

Adult↗

PubMed2003

Systems-level studies of movement disorders in dystonia and Parkinson's disease.

For many years pathophysiological studies on patients with movement disorders were viewed as inferior to those in animal models because, given the complexity of dealing with the complete interconnected CNS, it was difficult to assign any particular physiological abnormality exclusively to the site of a known lesion. More recently this has come to be seen as an advantage. All the articles reviewed below focus on how healthy parts of the CNS react to damage at a distance, with the result that we are now beginning to have much more insight into how these reactions both compensate and exacerbate the primary deficit.

Dystonia↗