Somatosensory disinhibition and frontal alien hand signs following medial frontal damage.

We report augmentation of somatosensory evoked potentials (SEP) in a patient with frontal alien hand signs after left medial frontal lobe damage. The SEP components occurring later than 30 msec post stimuli were enhanced over the parietal and frontal scalp sites of the lesioned hemisphere. This finding suggests that deficits in inhibitory control of somatosensory processing in parietal and frontal lobes contributes in some way to frontal alien hand signs.     

Somatosensory temporal discrimination tested in patients receiving botulinum toxin injection for cervical dystonia

We designed this study to find out more about the relationship between the sensory effects of Botulinum toxin type A (BTX) and the clinical benefits of BTX therapy in patients with cervical dystonia (CD). In 24 patients with CD, we tested sensory temporal discrimination (STD) in the affected and two unaffected body regions (neck, hand, and eye) before and 1 month after BTX injection. In 8 out of the 24 patients with CD, STDT values were tested bilaterally in the three body regions before, 1 and 2 months after BTX injection. As expected, STD testing disclosed altered STD threshold values in all three body regions tested (affected and unaffected by dystonic spasms) in patients with CD. STD threshold values remained unchanged at all time points of the follow‐up in all CD patients. The lack of BTX‐induced effects on STD thresholds suggests that STD recruits neural structures uninvolved in muscle spindle afferent activation. © 2010 Movement Disorder Society     

Somatosensory cortical activation in cervical dystonia and its modulation with botulinum toxin: an fMRI study

Converging data on focal dystonias suggest a widespread disorder of somatosensory processing. The aims of our study were, first, to assess somatosensory activation patterns in cervical dystonia (CD) beyond the representation of the affected body parts and, second, to search for task-related activation changes induced by botulinum toxin type-A (BoNT-A) therapy. Functional magnetic resonance imaging (MRI) during electrical median nerve stimulation was employed in seven CD patients and nine controls; the examination was repeated 4 weeks after BoNT-A application to dystonic neck muscles. The pretreatment activation map of patients showed activation in the contralateral primary somatosensory cortex, but missing activation in the secondary somatosensory cortex and insula, in contrast to controls and patients after treatment. Clinically significant effect of BoNT-A therapy was associated with a significant increase of BOLD response in the contralateral secondary somatosensory, insular, and inferior parietal cortices. The posttreatment somatosensory maps of patients did not significantly differ from controls. This study has brought evidence of widespread disruption of somatosensory processing in CD and its modification with BoNT-A therapy.     

Corticospinal disinhibition in paroxysmal kinesigenic dyskinesia.

OBJECTIVE: To investigate the underlying mechanism responsible for paroxysmal kinesigenic dyskinesia (PKD). METHODS: We performed a transcranial magnetic stimulation (TMS) study in 12 drug-na?ve patients with PKD and 10 healthy volunteers. TMS parameters included resting motor threshold, recruitment curve of motor evoked potential amplitudes, short intracortical inhibition and facilitation, long intracortical inhibition (LICI), and silent period. We also measured compound muscle action potential. RESULTS: LICI, representing GABA-mediated inhibition, was significantly reduced in the patients (P = 0.033), while results for all other TMS parameters tested were comparable between the two groups. CONCLUSIONS AND SIGNIFICANCE: These results suggest that a specific type of corticospinal inhibitory mechanism is impaired in patients with PKD.     

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.     

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.     

Smothering dystonia in a patient with oromandibular dystonia.

A case report is presented of a patient with pathologically confirmed striatonigral degeneration who experienced episodic syncope as a result of oromandibular dystonia obstructing inhalation through her mouth and nose.     

Somatosensory findings in postherpetic neuralgia.

Somatic sensory perception thresholds (warm, cold, hot pain, touch, pinprick, vibration, two-point discrimination), allodynia and skin temperature were assessed in the affected area of 42 patients with unilateral postherpetic neuralgia (PHN) and 20 patients who had had unilateral shingles not followed by PHN (NoPHN), and in the mirror-image area on the other side. There was no difference between the two groups for age or length of time after the acute herpes zoster infection. The PHN group showed significant changes in all sensory threshold measurements when the affected area was compared with the mirror-image area on the unaffected side, while the NoPHN group exhibited no threshold changes. Mechanical allodynia was present in 87% of the PHN group; half of the 12 patients with ophthalmic PHN showed extension of allodynia to the maxillary distribution. No differences in skin temperature were recorded between affected and unaffected regions in either group. Our findings show a deficit of sensory functions mediated by both large and small primary afferent fibres and also suggest major central involvement in the pathophysiology of the condition. If PHN does not occur following acute herpes zoster, recovery of neural functions appears to be good.     

Somatosensory evoked potentials in syringomyelia.

The two types of upper limb somatosensory evoked potential abnormality observed in nine patients with syringomyelia were reduced amplitude or absent cervical potentials and an abnormal central conduction time. Although this pattern of abnormalities resembles that observed in other intrinsic spinal cord lesions, it differs from peripheral nerve diseases and cervical radiculopathy in which the central conduction time is normal.     

Tizanidine in cranial dystonia.

Recent electrophysiological studies in patients with cranial dystonia (CD) have demonstrated evidence for hyperactivity of brainstem interneurons. Tizanidine (Tz), a centrally acting skeletal muscle relaxant, is thought to act by antagonizing the activity of excitatory interneurons which mediate hypertonic processes (e.g. spasticity). Theoretically this agent may be effective in patients with CD. Ten patients were enrolled in an open-label study with a single-blind placebo wash-in. Eight patients tolerated doses of between 28-36 mg per day. For the most part tizanidine was ineffective for the symptoms of CD. This failure suggests that the reported brainstem interneuronal disturbances may not be altered by Tz. Further studies using concomitant electrophysiological assessment would be necessary to assess this possibility. Alternatively, these disturbances may not be a principle cause of the dystonic movements. The finding of similar changes in other basal ganglia diseases lacking CD (e.g. Parkinson's disease) favours this latter explanation.     

Cognitive disinhibition and socioemotional functioning in Alzheimer's disease.

Individuals with Alzheimer's disease (AD) experience difficulties with socioemotional functioning, and it has been proposed that cognitive disinhibition may be one potential mechanism that contributes to difficulties in this area. To test this possibility, twenty individuals with AD and 20 demographically matched controls were administered self-report measures of depression, emotion regulation and empathy, in addition to a behavioral measure that has proven to be very sensitive to inhibitory failures (the Hayling Sentence Completion Test). Relative to controls AD participants exhibited increased inhibitory failures on the Hayling, and self-reported significantly reduced cognitive empathy, but did not differ with respect to affective empathy, depression or perceived capacity for emotion regulation. Controlling for general cognitive status, in the AD (but not the control) group, reduced cognitive inhibition was associated with lower levels of depression. The theoretical and practical implications of these results are discussed.     

Direct demonstration of transcallosal disinhibition in language networks.

Neuroimaging studies in right-handed patients with left hemisphere brain lesions have demonstrated a shift of language activity from left to right inferior frontal gyrus (IFG). This shift may be caused by greater right hemisphere dominance before the injury or by reduced inhibitory activity of the injured left hemisphere. We simulated a brain lesion applying transcranial -magnetic stimulation over left IFG in normal subjects, while simultaneously measuring language activity with positron -emission tomography. Interference with transcranial -magnetic stimulation decreased activity in left and increased it in right IFG in all subjects. We thus demonstrate for the first time that a rightward shift of language activity is caused by the brain lesion and not by greater right-hemisphere dominance, thus supporting the hypothesis of reduced transcallosal inhibition.