Transcranial Magnetic Stimulation and Cognitive Impairment

With transcranial magnetic stimulation (TMS), the motor system in neuropsychiatric disorders has extensively been investigated, and effects of certain pharmacological agents have been monitored. The most consistent finding in neuropsychiatric disorders is a significant reduction of short-latency afferent inhibition (SAI). SAI provides a reliable biomarker of cortical cholinergic dysfunction in neuropsychiatric disorders. Cortical hyperexcitability and asymptomatic motor cortex functional reorganization in the early stages of neuropsychiatric disorders have been demonstrated by TMS. Together with high-density EEG TMS and paired-associative stimulation, TMS showed impaired cortical plasticity and functional connectivity across different neural networks in neuropsychiatric disorders. Neuromodulatory techniques, especially as repetitive TMS (rTMS), hold promise as a therapeutic tool for cognitive rehabilitation because rTMS can enhance cognitive functions in neuropsychiatric disorders

Deactivation of the Default Mode Network as a Marker of Impaired Consciousness: An fMRI Study

Diagnosis of patients with a disorder of consciousness is very challenging. Previous studies investigating resting state networks demonstrate that 2 main features of the so-called default mode network (DMN), metabolism and functional connectivity, are impaired in patients with a disorder of consciousness. However, task-induced deactivation – a third main feature of the DMN – has not been explored in a group of patients. Deactivation of the DMN is supposed to reflect interruptions of introspective processes. Seventeen patients with unresponsive wakefulness syndrome (UWS, former vegetative state), 8 patients in minimally conscious state (MCS), and 25 healthy controls were investigated with functional magnetic resonance imaging during a passive sentence listening task. Results show that deactivation in medial regions is reduced in MCS and absent in UWS patients compared to healthy controls. Moreover, behavioral scores assessing the level of consciousness correlate with deactivation in patients. On single-subject level, all control subjects but only 2 patients in MCS and 6 with UWS exposed deactivation. Interestingly, all patients who deactivated during speech processing (except for one) showed activation in left frontal regions which are associated with conscious processing. Our results indicate that deactivation of the DMN can be associated with the level of consciousness by selecting those who are able to interrupt ongoing introspective processes. In consequence, deactivation of the DMN may function as a marker of consciousness

PLoS ONE / Deactivation of the default mode network as a marker of impaired consciousness : an fMRI study

Diagnosis of patients with a disorder of consciousness is very challenging. Previous studies investigating resting state networks demonstrate that 2 main features of the so-called default mode network (DMN), metabolism and functional connectivity, are impaired in patients with a disorder of consciousness. However, task-induced deactivation a third main feature of the DMN has not been explored in a group of patients. Deactivation of the DMN is supposed to reflect interruptions of introspective processes. Seventeen patients with unresponsive wakefulness syndrome (UWS, former vegetative state), 8 patients in minimally conscious state (MCS), and 25 healthy controls were investigated with functional magnetic resonance imaging during a passive sentence listening task. Results show that deactivation in medial regions is reduced in MCS and absent in UWS patients compared to healthy controls. Moreover, behavioral scores assessing the Level of consciousness correlate with deactivation in patients. On single-subject level, all control subjects but only 2 patients in MCS and 6 with UWS exposed deactivation. Interestingly, all patients who deactivated during speech processing (except for one) showed activation in left frontal regions which are associated with conscious processing. Our results indicate that deactivation of the DMN can be associated with the level of consciousness by selecting those who are able to interrupt ongoing introspective processes. In consequence, deactivation of the DMN may function as a marker of consciousness

Functional magnetic resonance imaging under anaesthesia of a patient with severe chronic disorders of consciousness

Clinical case: We report on a 19-year old male patient who is recovering from near-drowning. The patient was admitted for re-evaluation in a Minimally Conscious State. Method: A regular functional Magnetic Resonance Imaging was not possible due to complex motor tics of the patient with sudden flexion and extension movements of arms and legs as well as opisthotonic retroflexion of the head and trunk. Thus, the patient was anaesthetised and functional Magnetic Resonance Imaging was performed under general anaesthesia which was introduced and maintained with Sevoflorane and Fentanyl provided analgesia. Four functional runs were performed and the patients responses were recorded. During each one of these runs one extremity (dorsum manus or pedis) was stimulated with a brush with an operator-paced frequency of about 2Hz. Results and conclusion: Clear responses were found in the somatosensory cortex contra lateral within the post central gyrus during stimulation of the left hand. Considering the other three extremities no significant responses were found. Nevertheless, we conclude that a functional Magnetic Resonance Imaging under anaesthesia is possible for patients with severe chronic disorders of consciousness and brain areas responding to stimuli can be detected.(VLID)270631

Modulation of motor cortex excitability by different levels of whole-hand afferent electrical stimulation

h i g h l i g h t s We aim to identify optimal parameters for hand electrical stimulation to be used in neurorehabilitation. MG stimulation at a sensory level of 50 Hz and a motor level of 2 Hz proved to be effective. The induced motor cortical excitability increase lasts for a period of 1h post stimulation. a b s t r a c t Objective: In a previous transcranial magnetic stimulation (TMS) study we demonstrated that suprathreshold mesh-glove (MG) whole-hand stimulation elicits lasting changes in motor cortical excitability. Currently, there is no consensus with regard to the optimal parameters for the induction of sensorimotor cortical plasticity using peripheral electrical stimulation. Thus, in the present study we explore the modulatory effects of MG stimulation at different stimulus intensities and different frequencies in order to identify an optimal stimulation protocol. Methods: MG stimulation was performed on 12 healthy subjects in separate sessions at different stimulation levels: sub-sensory at 50 Hz, sensory at 50 Hz and motor at 2 Hz. To verify if stimulation at lower frequencies is less effective, an additional experiment at sensory level with 2 Hz was performed. TMS was used to assess motor threshold (MT), motor evoked potentials (MEPs) recruitment curve (RC), short latency intracortical inhibition (SICI) and intracortical facilitation (ICF) to paired-pulse TMS at baseline (T0), immediately after (T1) and 1 h (T2) after 30 min of MG stimulation. F-wave studies were performed to assess spinal motoneuron excitability. Results: MG stimulation at sub-sensory/50 Hz and sensory/2 Hz level determines no significant cortical excitability changes; at sensory/50 Hz level and at motor/2 Hz level we found decreased MT, increased MEP RC as well as reduced SICI and increased ICF at T1 and T2. Conclusions: MG stimulation at sensory/50 Hz and motor/2 Hz level induces similar long-lasting modulatory effects on motor cortical excitability. Both the strength of the corticospinal projections and the intracortical networks are influenced to the same extend. Significance: The study provides further evidence that stimulation intensity and frequency can independently modulate motor cortical plasticity. The selection of optimal stimulation parameters has potentially important implications for the neurorehabilitation of patients after brain damage (e.g. stroke, traumatic brain injury) with hand motor deficits

Between- and within-site variability of fMRI localizations

This study provides first data about the spatial variability of fMRI sensorimotor localizations when investigating the same subjects at different fMRI sites. Results are comparable to a previous patient study. We found a median between-site variability of about 6 mm independent of task (motor or sensory) and experimental standardization (high or low). An intraclass correlation coefficient analysis using data quality measures indicated a major influence of the fMRI site on variability. In accordance with this, within-site localization variability was considerably lower (about 3 mm). We conclude that the fMRI site is a considerable confound for localization of brain activity. However, when performed by experienced clinical fMRI experts, brain pathology does not seem to have a relevant impact on the reliability of fMRI localizations

Variability of clinical functional MR imaging results: a multicenter study

PURPOSE: To investigate intersite variability of clinical functional magnetic resonance (MR) imaging, including influence of task standardization on variability and use of various parameters to inform the clinician whether the reliability of a given functional localization is high or low. MATERIALS AND METHODS: Local ethics committees approved the study; all participants gave written informed consent. Eight women and seven men (mean age, 40 years) were prospectively investigated at three experienced functional MR sites with 1.5- (two sites) or 3-T (one site) MR. Nonstandardized motor and highly standardized somatosensory versions of a frequently requested clinical task (localization of the primary sensorimotor cortex) were used. Perirolandic functional MR variability was assessed (peak activation variability, center of mass [COM] variability, intraclass correlation values, overlap ratio [OR], activation size ratio). Data quality measures for functional MR images included percentage signal change (PSC), contrast-to-noise ratio (CNR), and head motion parameters. Data were analyzed with analysis of variance and a correlation analysis. RESULTS: Localization of perirolandic functional MR activity differed by 8 mm (peak activity) and 6 mm (COM activity) among sites. Peak activation varied up to 16.5 mm (COM range, 0.4-16.5 mm) and 45.5 mm (peak activity range, 1.8-45.5 mm). Signal strength (PSC, CNR) was significantly lower for the somatosensory task (mean PSC, 1.0% ± 0.5 [standard deviation]; mean CNR, 1.2 ± 0.4) than for the motor task (mean PSC, 2.4% ± 0.8; mean CNR, 2.9 ± 0.9) (P < .001, both). Intersite variability was larger with low signal strength (negative correlations between signal strength and peak activation variability) even if the task was highly standardized (mean OR, 22.0% ± 18.9 [somatosensory task] and 50.1% ± 18.8 [motor task]). CONCLUSION: Clinical practice and clinical functional MR biomarker studies should consider that the center of task-specific brain activation may vary up to 16.5 mm, with the investigating site, and should maximize functional MR signal strength and evaluate reliability of local results with PSC and CNR