[Neurophysiological evaluation using multimodal sensory evoked potentials in patients in coma: general aspects]

Sensory and motor cortical excitability changes induced by rTMS and sensory stimulation in stroke: A randomized clinical trial

Background

The ability to produce coordinated movement is dependent on dynamic interactions through transcallosal fibers between the two cerebral hemispheres of the brain. Although typically unilateral, stroke induces changes in functional and effective connectivity across hemispheres, which are related to sensorimotor impairment and stroke recovery. Previous studies have focused almost exclusively on interhemispheric interactions in the primary motor cortex (M1).

Objective

To identify the presence of interhemispheric asymmetry (ASY) of somatosensory cortex (S1) excitability and to investigate whether S1 repetitive transcranial magnetic stimulation (rTMS) combined with sensory stimulation (SS) changes excitability in S1 and M1, as well as S1 ASY, in individuals with subacute stroke.

Methods

A randomized clinical trial. Participants with a single episode of stroke, in the subacute phase, between 35 and 75 years old, were allocated, randomly and equally balanced, to four groups: rTMS/sham SS, sham rTMS/SS, rTMS/SS, and sham rTMS/Sham SS. Participants underwent 10 sessions of S1 rTMS of the lesioned hemisphere (10 Hz, 1,500 pulses) followed by SS. SS was applied to the paretic upper limb (UL) (active SS) or non-paretic UL (sham SS). TMS-induced motor evoked potentials (MEPs) of the paretic UL and somatosensory evoked potential (SSEP) of both ULs assessed M1 and S1 cortical excitability, respectively. The S1 ASY index was measured before and after intervention. Evaluator, participants and the statistician were blinded.

Results

Thirty-six participants divided equally into groups (nine participants per group). Seven patients were excluded from MEP analysis because of failure to produce consistent MEP. One participant was excluded in the SSEP analysis because no SSEP was detected. All somatosensory stimulation groups had decreased S1 ASY except for the sham rTMS/Sham SS group. When compared with baseline, M1 excitability increased only in the rTMS/SS group.

Conclusion

S1 rTMS and SS alone or in combination changed S1 excitability and decreased ASY, but it was only their combination that increased M1 excitability.

Clinical trial registration

clinicaltrials.gov, identifier (NCT03329807).

Somatosensory evoked potentials in clinical practice: a review

The authors present a review of the current use of somatosensory evoked potentials (SSEPs) in neurological practice as a non-invasive neurophysiological technique. For this purpose we have reviewed articles published in English or Portuguese in the PubMed and LILACS databases. In this review, we address the role of SSEPs in neurological diseases that affect the central nervous system and the peripheral nervous system, especially in demyelinating diseases, for monitoring coma, trauma and the functioning of sensory pathways during surgical procedures. The latter, along with new areas of research, has become one of the most important applications of SSEPs.

Post-traumatic apallic syndrome following head injury. Part 1: clinical characteristics

Epidemiological studies made within the western countries indicate an incidence of 200-300 traumatic head injuries per 100 000 residents each year. Severe head injuries account for 5-25% of all head injuries; 10-14% of all severe head-injured patients develop into a vegetative state, in which a sleep-wake rhythm is apparent, but however in which there is no evidence of awakeness or reactivity to the environment. The most commonly used labels, in the German and international literature, for these patients are 'vegetative state', 'apallic syndrome' and 'coma vigile'. This clinical characterization is not sufficient. It is necessary to employ additional criteria to distinguish subsets of vegetative patients e.g. computerized tomography, magnetic resonance imaging, single photon emission tomography, electroencephalography, brainstem reflexes, evoked potentials, assessment scales, age, premorbid brain disorders. Diagnostic and prognostic parameters must form the basis for various decisions relating to patients' care and intervention.

[Related observations for the use of mounting between neck posterior and scalp in evoked potentials by median nerve stimulation]

Somatosensory evoked potentials after stimulation of the median nerve were obtained in a group of normal individuals. The components obtained between 12 and 22 ms were analysed with cephalic and non-cephalic references. It is shown that the P13-14 complex is the major contributor for the amplitude of the N13 component recorded with electrodes between the posterior neck and the scalp. It has not been possible to detect differences in amplitude or latencies for the components N18 and P22 recorded between FZ-non cephalic and C6-FZ. Implications of these findings to clinical interpretations of the responses are discussed.