Biomedical subjects

Hiroyuki Oya

Publications and source records attributed to Hiroyuki Oya.

7 recordsLinked to original sources

PubMed2006

Functional connections between auditory cortical fields in humans revealed by Granger causality analysis of intra-cranial evoked potentials to sounds: comparison of two methods.

Knowledge of neural interactions amongst cortical sites is important for understanding higher brain function. We studied such interactions using Granger causality (GC) to analyze auditory event-related potentials (ERPs) recorded directly and simultaneously from two physiologically identified and functionally interconnected auditory areas of cerebral cortex in human neurosurgical patients. Two methods of GC analysis were used and the results compared. Both approaches involved adaptive autoregressive modeling but differed from each other in other ways. Results obtained by using the two methods also differed. Fewer false-positive results were obtained using the method that suppressed the ERP non-stationarity and that expressed the GC as the sum of model coefficients, which suggests that this is the more appropriate approach for analyzing ERPs recorded directly from the human cortex.

Auditory Cortex↗

PubMed2005

Electrophysiological correlates of reward prediction error recorded in the human prefrontal cortex.

Lesion and functional imaging studies have shown that the ventromedial prefrontal cortex is critically involved in the avoidance of risky choices. However, detailed descriptions of the mechanisms that underlie the establishment of such behaviors remain elusive, due in part to the spatial and temporal limitations of available research techniques. We investigated this issue by recording directly from prefrontal depth electrodes in a rare neurosurgical patient while he performed the Iowa Gambling Task, and we concurrently measured behavioral, autonomic, and electrophysiological responses. We found a robust alpha-band component of event-related potentials that reflected the mismatch between expected outcomes and actual outcomes in the task, correlating closely with the reward-related error obtained from a reinforcement learning model of the patient's choice behavior. The finding implicates this brain region in the acquisition of choice bias by means of a continuous updating of expectations about reward and punishment.

Choice Behavior↗

PubMed2005

Analysis of single-unit responses to emotional scenes in human ventromedial prefrontal cortex.

Lesion and functional imaging studies in humans have shown that the ventral and medial prefrontal cortex is critically involved in the processing of emotional stimuli, but both of these methods have limited spatiotemporal resolution. Conversely, neurophysiological studies of emotion in nonhuman primates typically rely on stimuli that do not require elaborate cognitive processing. To begin bridging this gap, we recorded from a total of 267 neurons in the left and right orbital and anterior cingulate cortices of four patients who had chronically implanted depth electrodes for monitoring epilepsy. Peristimulus activity was recorded to standardized, complex visual scenes depicting neutral, pleasant, or aversive content. Recording locations were verified with postoperative magnetic resonance imaging. Using a conservative, multistep statistical evaluation, we found significant responses in 56 neurons; 16 of these were selective for only one emotion class, most often aversive. The findings suggest sparse and widely distributed processing of emotional value in the prefrontal cortex, with a predominance of responses to aversive stimuli.

Action Potentials↗

PubMed2004

Intracortical responses in human and monkey primary auditory cortex support a temporal processing mechanism for encoding of the voice onset time phonetic parameter.

This study tests the hypothesis that temporal response patterns in primary auditory cortex are potentially relevant for voice onset time (VOT) encoding in two related experiments. The first experiment investigates whether temporal responses reflecting VOT are modulated in a way that can account for boundary shifts that occur with changes in first formant (F1) frequency, and by extension, consonant place of articulation. Evoked potentials recorded from Heschl's gyrus in a patient undergoing epilepsy surgery evaluation are examined. Representation of VOT varies in a manner that reflects the spectral composition of the syllables and the underlying tonotopic organization. Activity patterns averaged across extended regions of Heschl's gyrus parallel changes in the subject's perceptual boundaries. The second experiment investigates whether the physiological boundary for detecting the sequence of two acoustic elements parallels the psychoacoustic result of approximately 20 ms. Population responses evoked by two-tone complexes with variable tone onset times (TOTs) in primary auditory cortex of the monkey are examined. Onset responses evoked by both the first and second tones are detected at a TOT separation as short as 20 ms. Overall, parallels between perceptual and physiological results support the relevance of a population-based temporal processing mechanism for VOT encoding.

Animals↗

PubMed2004

A functional connection between inferior frontal gyrus and orofacial motor cortex in human.

The inferior frontal gyrus (IFG) of humans is known to play a critical role in speech production. The IFG is a highly convoluted and cytoarchitectonically diverse structure, classically forming 3 subgyri. It is reasonable to speculate that during speaking the IFG, or some portion of it, influences by corticocortical connections the orofacial representational area of primary motor cortex. To test the hypothesis that such corticocortical connections exist, electrical-stimulation tract tracing experiments were performed intraoperatively on 14 human subjects undergoing surgical treatment of medically intractable epilepsy. Bipolar electrical stimulation was applied to sites on the IFG, while the resulting evoked potentials were recorded from orofacial motor cortex, using a multichannel recording array. Stimulation of the IFG evoked polyphasic waveforms on motor cortex of both language-dominant and -nondominant hemispheres. The evoked waveforms had consistent features across subjects. The responses were seen in discrete regions on precentral cortex. Stimulation of motor cortex also evoked responses on portions of IFG. The data provide evidence for a functional connection between the human IFG and orofacial motor cortex.

Adult↗

PubMed2003

A device for cooling localized regions of human cerebral cortex. Technical note.

Neurosurgeons use invasive mapping methods during surgery to understand the functional neuroanatomy of patients. Electrical stimulation methods are used routinely for the temporary disruption of focal regions of cerebral cortex so that the surgeon may infer the functional role of the brain site being stimulated. Although it is an efficient and useful method, modes of electrical stimulation mapping have significant limitations. Neuroscientists use focal cooling to effect a more controlled disruption of cortical functions in experimental animals, and in this report, the authors describe their experience using a device to achieve this same objective in patients undergoing neurosurgery. The cooling probe consists of a stainless steel chamber with thermocouples and electroencephalography (EEG) recording contacts. Active cooling is achieved by infusing chilled saline into the chamber when the cooling probe is positioned on the pial surface. Experiments were performed in 18 patients. Temperature gradient measurements indicate that the entire thickness of gray matter under the probe is cooled to temperatures that disrupt local synaptic activity. Statistically significant changes in spontaneous and stimulus-evoked EEG activity were consistently observed during cooling, providing clear evidence of reversible disruption of physiological functions. Preliminary findings during functional mapping of the Broca area demonstrated qualitative differences between the temporary neurological deficits induced by cooling and those caused by electrical stimulation. These findings indicate the safety and utility of the cooling probe as a neurosurgical research tool. Additional rigorously designed studies should be undertaken to correlate the effects of cooling, electrical stimulation, and focal lesioning.

Brain Mapping↗

PubMed2002

Electrophysiological responses in the human amygdala discriminate emotion categories of complex visual stimuli.

The human amygdala has been shown to participate in processing emotionally salient stimuli related to threat, danger, and aversion, data that have come primarily from functional imaging and lesion studies. Recording intracranial field potentials from five amygdalas in four patients with chronically implanted depth electrodes, we analyzed responses in the gamma frequency range, a region of the power spectrum thought to reflect especially the contribution of neuronal activity to cognitive processes. Significant changes in the power amplitude of responses were obtained selectively to visual images judged to look aversive but not to those judged to look pleasant or neutral. Several possible confounds were addressed: all four patients had been carefully selected so that the amygdalas from which recordings were obtained were distal to epileptogenic foci, making it likely that we recorded from healthy tissue, and the observed responses could not be attributed to luminance or color differences between the stimuli. A further analysis of differences in power between the high and low gamma bands revealed an additional structure that discriminated those stimuli related to bodily injury from those related to disgust. Despite the increased power amplitude in the gamma range, there was no stimulus-locked phase coherence. The observed responses in the gamma frequency range may reflect the role of the amygdala in binding perceptual representations of the stimuli with memory, emotional response, and modulation of ongoing cognition, on the basis of the emotional significance of the stimuli.

Adult↗