Naohisa Miyakawa

Intrasulcal electrocorticography in macaque monkeys with minimally invasive neurosurgical protocols.

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 primates 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.

Simultaneous recording of single-neuron activities and broad-area intracranial electroencephalography: electrode design and implantation procedure.

BACKGROUND: There has been growing interest in clinical single-neuron recording to better understand epileptogenicity and brain function. It is crucial to compare this new information, single-neuronal activity, with that obtained from conventional intracranial electroencephalography during simultaneous recording. However, it is difficult to implant microwires and subdural electrodes during a single surgical operation because the stereotactic frame hampers flexible craniotomy. OBJECTIVE: To describe newly designed electrodes and surgical techniques for implanting them with subdural electrodes that enable simultaneous recording from hippocampal neurons and broad areas of the cortical surface. METHODS: We designed a depth electrode that does not protrude into the dura and pulsates naturally with the brain. The length and tract of the depth electrode were determined preoperatively between the lateral subiculum and the lateral surface of the temporal lobe. A frameless navigation system was used to insert the depth electrode. Surface grids and ventral strips were placed before and after the insertion of the depth electrodes, respectively. Finally, a microwire bundle was inserted into the lumen of the depth electrode. We evaluated the precision of implantation, the recording stability, and the recording rate with microwire electrodes. RESULTS: Depth-microwire electrodes were placed with a precision of 3.6 mm. The mean successful recording rate of single- or multiple-unit activity was 14.8%, which was maintained throughout the entire recording period. CONCLUSION: We achieved simultaneous implantation of microwires, depth electrodes, and broad-area subdural electrodes. Our method enabled simultaneous and stable recording of hippocampal single-neuron activities and multichannel intracranial electroencephalography. ABBREVIATIONS: iEEG, intracranial electroencephalography LFP, local field potential

High-density multielectrode array with independently maneuverable electrodes and silicone oil fluid isolation system for chronic recording from macaque monkey

Chronic multielectrode recording has become a widely used technique in the past twenty years, and there are multiple standardized methods. As for recording with high-density array, the most common method in macaque monkeys is to use a subdural array with fixed electrodes. In this study, we utilized the electrode array with independently maneuverable electrodes arranged in high-density, which was originally designed for use on small animals, and redesigned it for use on macaque monkeys while maintaining the virtues of maneuverability and high-density. We successfully recorded single and multiunit activities from up to 49 channels in the V1 and inferior temporal (IT) cortex of macaque monkeys. The main change in the surgical procedure was to remove a 5 mm diameter area of dura mater. The main changes in the design were (1) to have a constricted layer of heavy silicone oil at the interface with the animal to isolate the electrical circuit from the cerebrospinal fluid, and (2) to have a fluid draining system that can shunt any potential postsurgical subcranial exudate to the extracranial space.

Sound Frequency Representation in the Auditory Cortex of the Common Marmoset Visualized Using Optical Intrinsic Signal Imaging

Abstract Natural sound is composed of various frequencies. Although the core region of the primate auditory cortex has functionally defined sound frequency preference maps, how the map is organized in the auditory areas of the belt and parabelt regions is not well known. In this study, we investigated the functional organizations of the core, belt, and parabelt regions encompassed by the lateral sulcus and the superior temporal sulcus in the common marmoset (Callithrix jacchus). Using optical intrinsic signal imaging, we obtained evoked responses to band-pass noise stimuli in a range of sound frequencies (0.5–16 kHz) in anesthetized adult animals and visualized the preferred sound frequency map on the cortical surface. We characterized the functionally defined organization using histologically defined brain areas in the same animals. We found tonotopic representation of a set of sound frequencies (low to high) within the primary (A1), rostral (R), and rostrotemporal (RT) areas of the core region. In the belt region, the tonotopic representation existed only in the mediolateral (ML) area. This representation was symmetric with that found in A1 along the border between areas A1 and ML. The functional structure was not very clear in the anterolateral (AL) area. Low frequencies were mainly preferred in the rostrotemplatal (RTL) area, while high frequencies were preferred in the caudolateral (CL) area. There was a portion of the parabelt region that strongly responded to higher sound frequencies (>5.8 kHz) along the border between the rostral parabelt (RPB) and caudal parabelt (CPB) regions.

Heterogeneous Redistribution of Facial Subcategory Information Within and Outside the Face-Selective Domain in Primate Inferior Temporal Cortex

Abstract The inferior temporal cortex (ITC) contains neurons selective to multiple levels of visual categories. However, the mechanisms by which these neurons collectively construct hierarchical category percepts remain unclear. By comparing decoding accuracy with simultaneously acquired electrocorticogram (ECoG), local field potentials (LFPs), and multi-unit activity in the macaque ITC, we show that low-frequency LFPs/ECoG in the early evoked visual response phase contain sufficient coarse category (e.g., face) information, which is homogeneous and enhanced by spatial summation of up to several millimeters. Late-induced high-frequency LFPs additionally carry spike-coupled finer category (e.g., species, view, and identity of the face) information, which is heterogeneous and reduced by spatial summation. Face-encoding neural activity forms a cluster in similar cortical locations regardless of whether it is defined by early evoked low-frequency signals or late-induced high-gamma signals. By contrast, facial subcategory-encoding activity is distributed, not confined to the face cluster, and dynamically increases its heterogeneity from the early evoked to late-induced phases. These findings support a view that, in contrast to the homogeneous and static coarse category-encoding neural cluster, finer category-encoding clusters are heterogeneously distributed even outside their parent category cluster and dynamically increase heterogeneity along with the local cortical processing in the ITC.

3D reconstruction of brain section images for creating axonal projection maps in marmosets

BACKGROUND The brain of the common marmoset (Callithrix jacchus) is becoming a popular non-human primate model in neuroscience research. Because its brain fiber connectivity is still poorly understood, it is necessary to collect and present connection and trajectory data using tracers to establish a marmoset brain connectivity database. NEW METHOD To visualize projections and trajectories of axons, brain section images were reconstructed in 3D by registering them to the corresponding block-face brain images taken during brain sectioning. During preprocessing, autofluorescence of the tissue was reduced by applying independent component analysis to a set of fluorescent images taken using different filters. RESULTS The method was applied to a marmoset dataset after a tracer had been injected into an auditory belt area to fluorescently label axonal projections. Cortical and subcortical connections were clearly reconstructed in 3D. The registration error was estimated to be smaller than 200 μm. Evaluation tests on ICA-based autofluorescence reduction showed a significant improvement in signal and background separation. COMPARISON WITH EXISTING METHODS Regarding the 3D reconstruction error, the present study shows an accuracy comparable to previous studies using MRI and block-face images. Compared to serial section two-photon tomography, an advantage of the proposed method is that it can be combined with standard histological techniques. The images of differently processed brain sections can be integrated into the original ex vivo brain shape. CONCLUSIONS The proposed method allows creating 3D axonal projection maps overlaid with brain area annotations based on the histological staining results of the same animal.

Category decoding from macaque anterior inferotemporal cortex with simultaneous electrocorticogram and multi-channel unit recording

In the mammalian retina, synaptic transmission from rods to rod bipolar cells is mediated by a metabotropic glutamate receptor 6. In the dark, rods release glutamate by which rod bipolar cells hyperpolarize; conversely, in response to light, reduced release of glutamate from rods opens a nonselective cation channel and depolarizes the rod bipolar cells, from which glutamate is released to post-synaptic AII amacrine cells. We found that an inter-event interval and an amplitude of EPSCs observed in AII cells dramatically increased with the temperature and that the current-time integral of the EPSCs at 35 ◦C was about 3-fold greater than that at 20 ◦C. The temperature dependent EPSCs should reflect glutamatergic input from rod bipolar cells because the EPSCs in AII cells were blocked by CNQX or L-AP4 regardless of the temperature, but not strychnine and bicuculline, and the reversal potential was near 0 mV. Recent studies have demonstrated that the non-selective cation channel expressed in rod bipolar cells was a transient receptor potential (TRP) subfamily, TRPM1 channel. These data raise the possibility that body temperature may expand the dynamic range of the membrane potential in rod bipolar cells by increasing the open probability of the TRPM1 channels.

Multiple column activity in macaque area TE can encode object identity across view angles

It is well known that stimuli presented outside the classical receptive field (CRF) of a visual cortical neuron suppress its activities. This effect has traditionally been considered as providing auxiliary modulations to the properties determined by the CRF. However, its roles and the spatial organization of this suppressive effect have not been clear. We have recently developed a new method for reconstructing the details of the CRF (center) and surround structures simultaneously. Based on the twodimensional maps obtained by this method, we tested an idea that these structures constitute next-stage processing units suitable for encoding high-order contours such as contrast or texture boundaries. The majority of the center-surround maps showed a variety of oriented organizations, and cell responses were selective for orientation of high-order contours. These results indicate that a population of neurons with surround suppression is able to represent higher-order forms defined by contrast or texture borders.