Mapping of sheep sensory cortex with a novel microelectrocorticography grid

Abstract

Microelectrocorticography (µECoG) provides insights into the cortical organization with high temporal and spatial resolution desirable for better understanding of neural information processing. Here we evaluated the use of µECoG for detailed cortical recording of somatosensory evoked potentials (SEPs) in an ovine model. The approach to the cortex was planned using an MRI-based 3D model of the sheep's brain. We describe a minimally extended surgical procedure allowing placement of two different µECoG grids on the somatosensory cortex. With this small craniotomy, the frontal sinus was kept intact, thus keeping the surgical site sterile and making this approach suitable for chronic implantations. We evaluated the procedure for chronic implantation of an encapsulated µECoG recording system. During acute and chronic recordings, significant SEP responses in the triangle between the ansate, diagonal, and coronal sulcus were identified in all animals. Stimulation of the nose, upper lip, lower lip, and chin caused a somatotopic lateral-to-medial, ipsilateral response pattern. With repetitive recordings of SEPs, this somatotopic pattern was reliably recorded for up to 16 weeks. The findings of this study confirm the previously postulated ipsilateral, somatotopic organization of the sheep's sensory cortex. High gamma band activity was spatially most specific in the comparison of different frequency components of the somatosensory evoked response. This study provides a basis for further acute and chronic investigations of the sheep's sensory cortex by characterizing its exact position, its functional properties, and the surgical approach with respect to macroanatomical landmarks.

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

“…μECoG may thus increase the information content of cortical recordings [5], as well as the spatial specificity of cortical stimulation. As demonstrated recently, μECoG also allows for the acquisition of biologically relevant signals with a high spectral bandwidth of up to at least 1 kHz [6]. that open-loop SPES elicited CCEPs in the somatosensory cortex of the sheep, and characterize spectral power changes elicited by closed-loop RPES.…”

“…The built-in stimulation circuit generates voltage-controlled pulses with a maximum voltage compliance of 18 V. In this study, one sheep (Ovis orientalis aries) was chronically implanted with the system, and the μECoG electrode array was placed subdurally on the somatosensory cortex (Figure 1a,b). The somatosensory cortex was located by means of cranial and anatomical landmarks described in studies investigating sheep cortices [20,21], and was based on a previous SEP study using an identical electrode array in acute and chronic implantations [6]. For a photograph and more details on the implant see [22], and for details on the chronic implantation procedure and anesthesia medication used in the experiments see [6].…”

“…The somatosensory cortex was located by means of cranial and anatomical landmarks described in studies investigating sheep cortices [20,21], and was based on a previous SEP study using an identical electrode array in acute and chronic implantations [6]. For a photograph and more details on the implant see [22], and for details on the chronic implantation procedure and anesthesia medication used in the experiments see [6]. All experiments in the present study were approved by the Animal Committee of the University of Freiburg and the Regierungspräsidium Freiburg, Baden-Wuerttemberg, and EU Directive 2010/63/EU was followed for all experiments.…”

An interspecies comparative study of invasive electrophysiological functional connectivity

“…Our examination of connectivity specifically in resting state enables comparison between species, independent of cross-species behavioral or performance discrepancies (Goulas et al, 2014;He, Snyder, Zempel, Smyth, & Raichle, 2008). In addition to the obvious relevance of nonhuman primate research to human neurophysiology, nonhuman primates and other large animal models are frequently used as analogs for humans, especially for electrode development (Gierthmuehlen et al, 2014;Kohler et al, 2017).…”

Computation of a high‐resolution MRI 3D stereotaxic atlas of the sheep brain

“…The first reported preclinical study was performed by Opdam et al (2002), concerning the localization of epileptic foci by functional (f)MRI and EEG. Further studies used anatomical MR images to plan surgical interventions for translational stroke (Dreyer et al, 2012), to achieve a stereotactic access of the brainstem (Staudacher et al, 2014), and to guide micro-electrocorticography grid implantation for the mapping of the sensory cortex in the sheep brain (Gierthmuehlen et al, 2014). Recently, Lee et al (2015) utilized routine human fMRI and diffusion tensor imaging (DTI) protocols on sheep brain.…”