A wide range of devices is used to obtain intracranial electrocorticography recordings in patients with medically refractory epilepsy, including subdural strip and grid electrodes and depth electrodes. Penetrating depth electrodes are required to access some brain regions, and 1 target site that presents a particular technical challenge is the first transverse temporal gyrus, or Heschl gyrus (HG). The HG is located within the supratemporal plane and has an oblique orientation relative to the sagittal and coronal planes. Large and small branches of the middle cerebral artery abut the pial surface of the HG and must be avoided when planning the electrode trajectory. Auditory cortex is located within the HG, and there are functional connections between this dorsal temporal lobe region and medial sites commonly implicated in the pathophysiology of temporal lobe epilepsy. At some surgical centers, depth electrodes are routinely placed within the supratemporal plane, and the HG, in patients who require intracranial electrocorticography monitoring for presumed temporal lobe epilepsy. Information from these recordings is reported to facilitate the identification of seizure patterns in patients with or without auditory auras. To date, only one implantation method has been reported to be safe and effective for placing HG electrodes in a large series of patients undergoing epilepsy surgery. This well-established approach involves inserting the electrodes from a lateral trajectory while using stereoscopic stereotactic angiography to avoid vascular injury. In this report, the authors describe an alternative method for implantation. They use frameless stereotaxy and an oblique insertion trajectory that does not require angiography and allows for the simultaneous placement of subdural grid arrays. Results in 19 patients demonstrate the safety and efficacy of the method.
"Details of electrode implantation and data collection have been described previously (Nourski et al., 2009; Reddy et al., 2010). In brief, filtered (1.6e1000 Hz bandpass, 12 dB/octave rolloff) and amplified (20Â) ECoG data were digitally recorded (sampling rate 12,207 Hz) from custom-designed hybrid depth electrode arrays (AdTech). "
[Show abstract][Hide abstract] ABSTRACT: Successful categorization of phonemes in speech requires that the brain analyze the acoustic signal along both spectral and temporal dimensions. Neural encoding of the stimulus amplitude envelope is critical for parsing the speech stream into syllabic units. Encoding of voice onset time (VOT) and place of articulation (POA), cues necessary for determining phonemic identity, occurs within shorter time frames. An unresolved question is whether the neural representation of speech is based on processing mechanisms that are unique to humans and shaped by learning and experience, or is based on rules governing general auditory processing that are also present in non-human animals. This question was examined by comparing the neural activity elicited by speech and other complex vocalizations in primary auditory cortex of macaques, who are limited vocal learners, with that in Heschl's gyrus, the putative location of primary auditory cortex in humans. Entrainment to the amplitude envelope is neither specific to humans nor to human speech. VOT is represented by responses time-locked to consonant release and voicing onset in both humans and monkeys. Temporal representation of VOT is observed both for isolated syllables and for syllables embedded in the more naturalistic context of running speech. The fundamental frequency of male speakers is represented by more rapid neural activity phase-locked to the glottal pulsation rate in both humans and monkeys. In both species, the differential representation of stop consonants varying in their POA can be predicted by the relationship between the frequency selectivity of neurons and the onset spectra of the speech sounds. These findings indicate that the neurophysiology of primary auditory cortex is similar in monkeys and humans despite their vastly different experience with human speech, and that Heschl's gyrus is engaged in general auditory, and not language-specific, processing.
Hearing research 06/2013; 305(1). DOI:10.1016/j.heares.2013.05.013 · 2.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Speech comprehension relies on temporal cues contained in the speech envelope, and the auditory cortex has been implicated as playing a critical role in encoding this temporal information. We investigated auditory cortical responses to speech stimuli in subjects undergoing invasive electrophysiological monitoring for pharmacologically refractory epilepsy. Recordings were made from multicontact electrodes implanted in Heschl's gyrus (HG). Speech sentences, time compressed from 0.75 to 0.20 of natural speaking rate, elicited average evoked potentials (AEPs) and increases in event-related band power (ERBP) of cortical high-frequency (70-250 Hz) activity. Cortex of posteromedial HG, the presumed core of human auditory cortex, represented the envelope of speech stimuli in the AEP and ERBP. Envelope following in ERBP, but not in AEP, was evident in both language-dominant and -nondominant hemispheres for relatively high degrees of compression where speech was not comprehensible. Compared to posteromedial HG, responses from anterolateral HG-an auditory belt field-exhibited longer latencies, lower amplitudes, and little or no time locking to the speech envelope. The ability of the core auditory cortex to follow the temporal speech envelope over a wide range of speaking rates leads us to conclude that such capacity in itself is not a limiting factor for speech comprehension.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 12/2009; 29(49):15564-74. DOI:10.1523/JNEUROSCI.3065-09.2009 · 6.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work, we show that electrophysiological responses during pitch perception are best explained by distributed activity in a hierarchy of cortical sources and, crucially, that the effective connectivity between these sources is modulated with pitch strength. Local field potentials were recorded in two subjects from primary auditory cortex and adjacent auditory cortical areas along the axis of Heschl's gyrus (HG) while they listened to stimuli of varying pitch strength. Dynamic causal modeling was used to compare system architectures that might explain the recorded activity. The data show that representation of pitch requires an interaction between nonprimary and primary auditory cortex along HG that is consistent with the principle of predictive coding.
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