Mapping human brain networks with cortico-cortical evoked potentials

Abstract

The cerebral cortex forms a sheet of neurons organized into a network of interconnected modules that is highly expanded in humans and presumably enables our most refined sensory and cognitive abilities. The links of this network form a fundamental aspect of its organization, and a great deal of research is focusing on understanding how information flows within and between different regions. However, an often-overlooked element of this connectivity regards a causal, hierarchical structure of regions, whereby certain nodes of the cortical network may exert greater influence over the others. While this is difficult to ascertain non-invasively, patients undergoing invasive electrode monitoring for epilepsy provide a unique window into this aspect of cortical organization. In this review, we highlight the potential for cortico-cortical evoked potential (CCEP) mapping to directly measure neuronal propagation across large-scale brain networks with spatio-temporal resolution that is superior to traditional neuroimaging methods. We first introduce effective connectivity and discuss the mechanisms underlying CCEP generation. Next, we highlight how CCEP mapping has begun to provide insight into the neural basis of non-invasive imaging signals. Finally, we present a novel approach to perturbing and measuring brain network function during cognitive processing. The direct measurement of CCEPs in response to electrical stimulation represents a potentially powerful clinical and basic science tool for probing the large-scale networks of the human cerebral cortex.

Mapping dynamical properties of cortical microcircuits using robotized TMS and EEG: Towards functional cytoarchitectonics

“…It has been shown to reflect a consistent aftereffect of the stimulation rather than a pure auditory or somatosensory artifact. Finally, such components have also been found in intracranial cortico-cortical evoked potentials after direct electrical stimulation of various areas (Keller et al, 2014). They could thus mainly reflect the activation of remote cortical and subcortical areas connected to the stimulation site.…”

“…Several studies using direct cortical electrical stimulation also showed that the properties of the neuronal responses depend a lot on the intrinsic cytoarchitecture or connectivity patterns of the stimulated area, in both animals (Luppino et al, 1991) and humans (Keller et al, 2014).…”

Evoked directional network characteristics of epileptogenic tissue derived from single pulse electrical stimulation

“…ERs occur each time a pulse is applied to the same electrode pair, and are thus deterministic. In cortico‐cortical evoked potential studies, this ER is known as the N1‐response (Enatsu, Piao, et al, 2012; Keller et al, 2014; Matsumoto et al, 2004, 2007) and the physiological networks derived from these N1‐responses have been investigated in, for example, the language and motor system (Matsumoto et al, 2004, 2007). …”

Closed-loop interaction with the cerebral cortex using a novel micro-ECoG-based implant: the impact of beta vs. gamma stimulation frequencies on cortico-cortical spectral responses

“…As they are perturbation-based, CCEPs can unequivocally show directed (causal) connectivity between remote areas [11,12], which is challenging to achieve by analysis of undisturbed brain dynamics. As of yet, the CCEP technique has been only rarely applied utilizing μECoG electrodes.…”

“…This well-established method allows one to unravel functional connectivity in the cortex [7][8][9][10][11][12] or subcortical regions [13], and recent studies used ECoG-based SPES in humans to investigate CCEPassociated changes in the spectral domain [14,15]. For reviews on studies investigating cortical connectivity by means of CCEPs see [16,17].…”