EEG to Identify Attempted Movement in Unresponsive Wakefulness Syndrome.

Assessment of consciousness following severe brain-injury is challenging. Our hypothesis is that electroencephalography (EEG) can provide information on awareness, in terms of oscillatory activity and network task-related modifications, in people with disorders of consciousness. Similar results were obtained with neuroimaging techniques; we aim at demonstrating the use of EEG, which is low cost and routinely implemented, to the same goal. Nineteen-channel EEG was recorded in 7 persons with unresponsive wakefulness syndrome (UWS) and in 10 healthy subjects during the execution of active (attempted movement) and passive motor tasks as well as 2 mental imagery tasks. Event-related synchronization/desynchronization (ERS/ERD), coherence and network parameters were calculated in delta (1-4 Hz), theta (4-8 Hz), alpha1 (8-10 Hz), alpha2 (10-12 Hz), and beta (13-30 Hz) ranges. In UWS subjects, passive movement induced a weak alpha2 ERD over contralateral sensorimotor area. During motor imagery, ERD was detected over the frontal and motor contralateral brain areas; during spatial imagery, ERS in lower alpha band over the right temporo-parietal regions was missing. In UWS, functional connectivity provided evidence of network disruption and isolation of the motor areas, which cannot dialog with adjacent network nodes, likely suggesting a diffuse structural alteration. Our findings suggest that people with a clinical diagnosis of UWS were able to modulate their brain activity when prompted to perform movement tasks and thus suggest EEG as a potential tool to support diagnosis of disorders of consciousness.

Selective attention impairment in amyotrophic lateral sclerosis.

Objective of this study was to evaluate attentional control mechanisms in amyotrophic lateral sclerosis (ALS) using an auditory event-related potentials (ERPs) paradigm. Fifteen mild to moderate ALS patients and 15 healthy controls were administered a brief neuropsychological test battery and an ERPs paradigm assessing selective attention. Four types of auditory stimuli were presented in random order: short standard (200 Hz, 200 ms), long standard (200 Hz, 500 ms), short deviant (1000 Hz, 200 ms) and long deviant (1000 Hz, 500 ms). Participants had to respond to the long deviant stimuli only. During the task the electroencephalogram (EEG) was recorded. The N200, P300 and re-orienting negativity (RON) ERP components were analysed. Compared to controls ALS patients showed reduced amplitudes and delayed latencies of N200, P300 and RON. These results could be attributable to both an alteration in change detection resulting in a reduction of the allocation and re-orientation of attentional resources or a general slowing or reduction of neural processing efficiency in the same system. The ERPs results support the hypothesis that ALS involves extramotor cognitive functions including auditory attentional processing at all processing stages, early (200 ms) and late (300-600 ms). These data prove the usefulness and sensitivity of the auditory ERPs in detection of cognitive functions in ALS patients.

Coherence and Consciousness: Study of Fronto-Parietal Gamma Synchrony in Patients with Disorders of Consciousness.

Evaluation of consciousness needs to be supported by the evidence of brain activation during external stimulation in patients with unresponsive wakefulness syndrome (UWS). Assessment of patients should include techniques that do not depend on overt motor responses and allow an objective investigation of the spontaneous patterns of brain activity. In particular, electroencephalography (EEG) coherence allows to easily measure functional relationships between pairs of neocortical regions and seems to be closely correlated with cognitive or behavioral measures. Here, we show the contribution of higher order associative cortices of patients with disorder of consciousness (N = 26) in response to simple sensory stimuli, such as visual, auditory and noxious stimulation. In all stimulus modalities an increase of short-range parietal and long-range fronto-parietal coherences in gamma frequencies were seen in the controls and minimally conscious patients. By contrast, UWS patients showed no significant modifications in the EEG patterns after stimulation. Our results suggest that UWS patients can not activate associative cortical networks, suggesting a lack of information integration. In fact, fronto-parietal circuits result to be connectively disrupted, conversely to patients that exhibit some form of consciousness. In the light of this, EEG coherence can be considered a powerful tool to quantify the involvement of cognitive processing giving information about the integrity of fronto-parietal network. This measure can represent a new neurophysiological marker of unconsciousness and help in determining an accurate diagnosis and rehabilitative intervention in each patient.

Transcranial direct current stimulation (tDCS) of Broca's area in chronic aphasia: a controlled outcome study.

BACKGROUND: In the last decade transcranial direct current stimulation (tDCS) has been introduced in aphasia post-stroke recovery as a tool for modulating neuroplasticity. However, it is still unclear whether tDCS should be applied at rest (off-line) or combined with behavioral treatment strategies (on-line), therefore, this study investigates the effect of repeated sessions of off-line tDCS on language recovery in post-stroke chronic aphasic patients. METHODOLOGY: Eight post-stroke patients with different type and degree of chronic aphasia underwent two weeks of off-line anodal tDCS (2 mA intensity for 20 min a day) on Broca's area and two weeks of sham stimulation as a control condition. Language recovery was measured assessing object and action naming abilities with a computerized picture naming task. RESULTS: No significant difference between anodal tDCS and sham stimulation, both for object and action naming tasks, was found. Descriptive analysis of single cases showed that after tDCS only one patient improved substantially on action naming task. CONCLUSION: With the exception of one patient, the overall results suggest that in chronic aphasic patients the off-line tDCS protocol applied in this study is not effective in improving noun and verb naming abilities.

Working memory in amyotrophic lateral sclerosis: auditory event-related potentials and neuropsychological evidence.

Aim of this study is to investigate working memory functions in nondemented patients with amyotrophic lateral sclerosis (ALS) using neuropsychological testing and auditory event-related potentials. Twenty-four patients with ALS and 17 age- and education-matched controls underwent a comprehensive neuropsychological assessment, with particular emphasis on working memory functions. Event-related potentials were assessed with an active auditory oddball paradigm. In a subsample (67%) of patients with ALS, the neuropsychological assessment revealed impaired performance on working memory tests (semantic and letter verbal fluency, modified card sorting test, trail making test, digit span, Corsi blocks tapping test, and prose memory). The analysis of event-related potentials showed a significant delay of the N100, P200, and N200 latency in ALS compared with controls. Correlation analysis showed a relation between clinical parameters (disease duration and functional rating scale) and neuropsychological test results (letter fluency and trail making test) and between disease duration and P300 amplitude. The neuropsychological and event-related potentials profile of patients with ALS at an average is consistent with a mild dysfunction of the central executive component of working memory. In conclusion, the results support previously published reports that indicate the involvement of the extramotor functions in a significant subsample of ALS.