Abstract
Electrocorticography (ECoG), multichannel brain-surface recording and stimulation with probe electrode arrays, has become a potent methodology not only for clinical neurosurgery but also for basic neuroscience using animal models. The highly evolved primate's brain has deep cerebral sulci, and both gyral and intrasulcal cortical regions have been implicated in important functional processes. However, direct experimental access is typically limited to gyral regions, since placing probes into sulci is difficult without damaging the surrounding tissues. Here we describe a novel methodology for intrasulcal ECoG in macaque monkeys. We designed and fabricated ultra-thin flexible probes for macaques with micro-electro-mechanical systems technology. We developed minimally invasive operative protocols to implant the probes by introducing cutting-edge devices for human neurosurgery. To evaluate the feasibility of intrasulcal ECoG, we conducted electrophysiological recording and stimulation experiments. First, we inserted parts of the Parylene-C-based probe into the superior temporal sulcus to compare visually evoked ECoG responses from the ventral bank of the sulcus with those from the surface of the inferior temporal cortex. Analyses of power spectral density and signal-to-noise ratio revealed that the quality of the ECoG signal was comparable inside and outside of the sulcus. Histological examination revealed no obvious physical damage in the implanted areas. Second, we placed a modified silicone ECoG probe into the central sulcus and also on the surface of the precentral gyrus for stimulation. Thresholds for muscle twitching were significantly lower during intrasulcal stimulation compared to gyral stimulation. These results demonstrate the feasibility of intrasulcal ECoG in macaques. The novel methodology proposed here opens up a new frontier in neuroscience research, enabling the direct measurement and manipulation of electrical activity in the whole brain.
Highlights
Cerebral cortex is intricately folded in many primate species
Four to five branches of the probe were implanted into the superior temporal sulcus (STS) (Figures 3C,D), whereas other branches and the trunk of the probe were placed on the gyral surface of the inferior temporal gyrus (ITG)
It is becoming clear in the neuroprosthetic literature that the use of microelectrodes for the recording of single cell signals that drive artificial effectors has some problems (Polikov et al, 2005; Chao et al, 2010)
Summary
Cerebral cortex is intricately folded in many primate species. In humans, two-thirds of the cerebral cortex is buried in grooves, known as the cerebral sulci, whereas only one-third of the cortex is exposed in the cerebral gyri (Ribas, 2010). Functional magnetic resonance imaging (fMRI) and positron emission tomography have revealed neural activation related to important functions such as cognition and attention in intrasulcal as well as gyral regions of the cerebral cortex (Tsao et al, 2003; Beauchamp et al, 2004; Koyama et al, 2004). These neuroimaging techniques, have difficulty obtaining precise spatiotemporal profiles of intrasulcal activity simultaneously with millimeter source localization and millisecond temporal resolution. Direct access to the intrasulcal cortices without damaging the surrounding tissues could enable stable recording from and stimulation to these regions in physiological conditions, advancing our understanding of the fundamental cerebral functions in situ
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