Electrical brain stimulation in epilepsy

Because it provides functional assessment of the central nervous system, the domain of clinical neurophysiology (CN) is similar to that of clinical examination and complementary to that of imaging techniques. CN has two major advantages over clinical examination: it is still feasible in curarized patients and it is more quantitative and thus more amenable to follow-up studies. CN consists of EEG and evoked potentials (EPs). EEG provides online assessment and remains unique tool to evidence or (in some limits) rule out epilepsy. EPs summarize brain or brainstem activity over the time needed for their recording. These are subdivided into exogenous (visual, auditory, somatosensory) and cognitive EPs. A complete CN examination generates a huge set of parameters, which we synthesize under the form of two indices: the index of global cortical function (IGCF) and the index of brainstem conduction (IBSC). The way to interpret EPs varies as a function of coma aetiology. In anoxic coma, IBSC usually remains unchanged so that prognosis largely relies on IGCF. Roughly, marked IGCF alterations have an ominous prognostic value while the preservation of cognitive EPs implies a very high probability of consciousness recovery. In traumatic coma, the overall neurological prognosis relies relatively more on the IBSC than the IFGC. It has also become clear that EPs are the best brain-death confirmatory tool. Although data obtained in adults can be largely extrapolated to paediatrics, two factors should be taken into account: immaturity, which influences both norms and brain sensitivity to the pathophysiological processes that are met in the ICU, and technical limitations that can influence the examination strategies.