The difference between electrical microstimulation and direct electrical stimulation – towards new opportunities for innovative functional brain mapping?

Abstract

<jats:title>Abstract</jats:title><jats:p>Both electrical microstimulation (EMS) and direct electrical stimulation (DES) of the brain are used to perform functional brain mapping. EMS is applied to animal fundamental neuroscience experiments, whereas DES is performed in the operating theatre on neurosurgery patients. The objective of the present review was to shed new light on electrical stimulation techniques in brain mapping by comparing EMS and DES. There is much controversy as to whether the use of DES during wide-awake surgery is the ‘gold standard’ for studying the brain function. As part of this debate, it is sometimes wrongly assumed that EMS and DES induce similar effects in the nervous tissues and have comparable behavioural consequences. In fact, the respective stimulation parameters in EMS and DES are clearly different. More surprisingly, there is no solid biophysical rationale for setting the stimulation parameters in EMS and DES; this may be due to historical, methodological and technical constraints that have limited the experimental protocols and prompted the use of empirical methods. In contrast, the gap between EMS and DES highlights the potential for new experimental paradigms in electrical stimulation for functional brain mapping. In view of this gap and recent technical developments in stimulator design, it may now be time to move towards alternative, innovative protocols based on the functional stimulation of peripheral nerves (for which a more solid theoretical grounding exists).</jats:p>

A measure of cortico-cortical potentials evoked by 10Hz direct electrical stimulation of the brain and by means of a differential recording mode of electrocorticographic signals

“…However previous studies were performed at a very low frequency (1 Hz) and although single-pulse stimuli can produce CCEPs and ACEPs, it has not been yet demonstrated that DES at higher frequency affects the whole network in the same manner [2,3]. In contrast, 100 ms seems to be a sufficient time-window that facilitates real-time averaging to detect these CCEPs and ACEPs for further on-line analysis of brain connectivity during the surgery.…”

“…Its use lowers the probability of resecting essential functional areas near or within the tumor. However, the electrophysiological effects of DES remain poorly understood, locally and at a more remote distance [2,3]. The investigation of this topic requires in part the recording of evoked potential.…”

Modeling subcortical white matter stimulation

“…As such, 5 functional mapping aids in the identification of non-operational tissues important to 6 excise, and the prevention of neuropsychological complications induced by the excision 7 1/13 of operational tissue and tracts (fasciculi of axons). Despite the demonstrated utility of 8 intra-operative functional mapping, there is no standard approach to choose the 9 electrode parameters that are mostly set empirically [31]. Parameters of electrical 10 stimulation include pulse shape, pulse duration (P W ), stimulus amplitude (I), (Fig.…”

“…1 B). Although bipolar biphasic stimulation is often used during 16 subcortical or cortical electrical stimulation [31], some clinical studies have also explored 17 cortical and subcortical responses using bipolar monophasic [13,30], monopolar 18 monophasic [10], and monopolar biphasic stimulation [10]. The effects of stimulation 19 parameters are difficult to assess experimentally, because closed-loop electrodes are not 20 routinely used for functional mapping and other fine assessments of the spatial-temporal 21 effects of stimulation parameters would require implantation of further electrodes used 22 only for research, and thus difficult to pass ethical review.…”

“…To study the 26 effects of stimulation parameters despite empirical limitations, computational modeling 27 of neural responses to stimulus-induced electric fields are commonly used, especially in 28 deep brain stimulation [2,18,20,27,33] but few have studied the effects of subcortical 29 stimulation [8,16,17]. Gomez-Tames et al [8] have recently assessed the influence of 30 electrode diameter, and inter-electrode distance, as well as bipolar versus monopolar 31 electrode using a head model with purely isotropic white matter. They show that for a 32 fixed current amplitude, monophasic monopolar stimulation had a broader activation 33 region that monophasic bipolar stimulation.…”