Frontal and temporal functional connections of the living human brain

Abstract

Connections between human temporal and frontal cortices were investigated by intracranial electroencephalographic responses to electrical stimulation with 1-ms single pulses in 51 patients assessed for surgery for treatment of epilepsy. The areas studied were medial temporal, entorhinal, lateral temporal, medial frontal, lateral frontal and orbital frontal cortices. Findings were assumed to be representative of human brain as no differences were found between epileptogenic and non-epileptogenic hemispheres. Connections between intralobar temporal and frontal regions were common (43-95%). Connections from temporal to ipsilateral frontal regions were relatively uncommon (seen in 0-25% of hemispheres). Connections from frontal to ipsilateral temporal cortices were more common, particularly from orbital to ipsilateral medial temporal regions (40%). Contralateral temporal connections were rare (< 9%) whereas contralateral frontal connections were frequent and faster, particularly from medial frontal to contralateral medial frontal (61%) and orbital frontal cortices (57%), and between both orbital cortices (67%). Orbital cortex receives profuse connections from the ipsilateral medial (78%) and lateral (88%) frontal cortices, and from the contralateral medial (57%) and orbital (67%) frontal cortices. The high incidence of intralobar temporal connections supports the presence of temporal reverberating circuits. Frontal cortex projects within the lobe and beyond, to ipsilateral and contralateral structures.

Physiology of functional and effective networks in epilepsy

“…Additionally, ictal onset patterns characterized by repetitive spiking show larger CCEPs amplitudes than those by focal paroxysmal fast activity. These results seem to contradict the conclusion by Lacruz et al (2007) that ipsilateral and contralateral connections between normal and epileptogenic hemispheres were similar. These findings may be reconciled by considering that the latter study only looked for the presence or absence of CCEPs responses, while those that found differences between ictal and normal cortex assessed the amplitude of evoked potentials.…”

Intrinsic functional architecture predicts electrically evoked responses in the human brain

“…CCEPs are elicited in response to single-pulse electrical stimulation of the cortex, with subdural electrodes implanted for the purpose of seizure localization (clinical information and demographics are presented in SI Table S1). CCEPs permit us to "electrically track" corticocortical neuronal connections in vivo by stimulating one cortical region and recording the evoked potentials at another location, because responses at the recorded site are the direct result of neuronal projections from the stimulation site (11)(12)(13). To obtain CCEPs, we administered repeated brief single-pulse electrical currents between adjacent electrodes and recorded the evoked electrophysiological responses at all other implanted electrode sites (Fig.…”

Electrical Stimulation of the Anterior Cingulate Gyrus Induces Responses Similar to K-complexes in Awake Humans

“…Patients with bilateral frontal electrodes were deliberately chosen because stimulating at extra-frontal structures in the total population of 269 patients did not induce responses remotely similar to K-complexes. For instance, SPES responses to hippocampal stimulation induces bilateral responses only in 5% of patients [34,45], and when they occur, they are grossly asymmetrical. Furthermore, even within the frontal lobes, the similarity between SPES responses and K-complexes is highly specific of stimulation of the dorso-caudal anterior cingulate or its underlying white matter (Table 2).…”

“…Indeed, the slow cortical oscillations involved in the genesis of K-complexes [3] appear to be intrinsically generated in cortical neurons [10]. Moreover, there are profuse bilateral connections between medial frontal cortices [34], which may be responsible for the bilateral cortical involvement seen during both, normal sleep K-complexes and electrically induced K-complexes [7]. In the generation of normal sleep K-complexes, subcortical structures could modulate cortical excitability, allowing for neuronal synchronization similar to that induced by focal stimulation of the anterior cingulate in our awake patients.…”