A Spatial Map of Onset and Sustained Responses to Speech in the Human Superior Temporal Gyrus.

To derive meaning from speech, we must extract multiple dimensions of concurrent information from incoming speech signals. That is, equally important to processing phonetic features is the detection of acoustic cues that give structure and context to the information we hear. How the brain organizes this information is unknown. Using data-driven computational methods on high-density intracranial recordings from 27 human participants, we reveal the functional distinction of neural responses to speech in the posterior superior temporal gyrus according to either onset or sustained response profiles. Though similar response types have been observed throughout the auditory system, we found novel evidence for a major spatial parcellation in which a distinct caudal zone detects acoustic onsets and a rostral-surround zone shows sustained, relatively delayed responses to ongoing speech stimuli. While posterior onset and anterior sustained responses are used substantially during natural speech perception, they are not limited to speech stimuli and are seen even for reversed or spectrally rotated speech. Single-electrode encoding of phonetic features in each zone depended upon whether the sound occurred at sentence onset, suggesting joint encoding of phonetic features and their temporal context. Onset responses in the caudal zone could accurately decode sentence and phrase onset boundaries, providing a potentially important internal mechanism for detecting temporal landmarks in speech and other natural sounds. These findings suggest that onset and sustained responses not only define the basic spatial organization of high-order auditory cortex but also have direct implications for how speech information is parsed in the cortex. VIDEO ABSTRACT.

Spatial resolution dependence on spectral frequency in human speech cortex electrocorticography.

OBJECTIVE: Electrocorticography (ECoG) has become an important tool in human neuroscience and has tremendous potential for emerging applications in neural interface technology. Electrode array design parameters are outstanding issues for both research and clinical applications, and these parameters depend critically on the nature of the neural signals to be recorded. Here, we investigate the functional spatial resolution of neural signals recorded at the human cortical surface. We empirically derive spatial spread functions to quantify the shared neural activity for each frequency band of the electrocorticogram. APPROACH: Five subjects with high-density (4 mm center-to-center spacing) ECoG grid implants participated in speech perception and production tasks while neural activity was recorded from the speech cortex, including superior temporal gyrus, precentral gyrus, and postcentral gyrus. The cortical surface field potential was decomposed into traditional EEG frequency bands. Signal similarity between electrode pairs for each frequency band was quantified using a Pearson correlation coefficient. MAIN RESULTS: The correlation of neural activity between electrode pairs was inversely related to the distance between the electrodes; this relationship was used to quantify spatial falloff functions for cortical subdomains. As expected, lower frequencies remained correlated over larger distances than higher frequencies. However, both the envelope and phase of gamma and high gamma frequencies (30-150 Hz) are largely uncorrelated (<90%) at 4 mm, the smallest spacing of the high-density arrays. Thus, ECoG arrays smaller than 4 mm have significant promise for increasing signal resolution at high frequencies, whereas less additional gain is achieved for lower frequencies. SIGNIFICANCE: Our findings quantitatively demonstrate the dependence of ECoG spatial resolution on the neural frequency of interest. We demonstrate that this relationship is consistent across patients and across cortical areas during activity.

Hierarchy of prediction errors for auditory events in human temporal and frontal cortex.

Predictive coding theories posit that neural networks learn statistical regularities in the environment for comparison with actual outcomes, signaling a prediction error (PE) when sensory deviation occurs. PE studies in audition have capitalized on low-frequency event-related potentials (LF-ERPs), such as the mismatch negativity. However, local cortical activity is well-indexed by higher-frequency bands [high-γ band (Hγ): 80-150 Hz]. We compared patterns of human Hγ and LF-ERPs in deviance detection using electrocorticographic recordings from subdural electrodes over frontal and temporal cortices. Patients listened to trains of task-irrelevant tones in two conditions differing in the predictability of a deviation from repetitive background stimuli (fully predictable vs. unpredictable deviants). We found deviance-related responses in both frequency bands over lateral temporal and inferior frontal cortex, with an earlier latency for Hγ than for LF-ERPs. Critically, frontal Hγ activity but not LF-ERPs discriminated between fully predictable and unpredictable changes, with frontal cortex sensitive to unpredictable events. The results highlight the role of frontal cortex and Hγ activity in deviance detection and PE generation.

Cortical theta wanes for language.

The role of low frequency oscillations in language areas is not yet understood. Using ECoG in six human subjects, we studied whether different language regions show prominent power changes in a specific rhythm, in similar manner as the alpha rhythm shows the most prominent power changes in visual areas. Broca's area and temporal language areas were localized in individual subjects using fMRI. In these areas, the theta rhythm showed the most pronounced power changes and theta power decreased significantly during verb generation. To better understand the role of this language-related theta decrease, we then studied the interaction between low frequencies and local neuronal activity reflected in high frequencies. Amplitude-amplitude correlations showed that theta power correlated negatively with high frequency activity, specifically across verb generation trials. Phase-amplitude coupling showed that during control trials, high frequency power was coupled to theta phase, but this coupling decreased significantly during verb generation trials. These results suggest a dynamic interaction between the neuronal mechanisms underlying the theta rhythm and local neuronal activity in language areas. As visual areas show a pronounced alpha rhythm that may reflect pulsed inhibition, language regions show a pronounced theta rhythm with highly similar features.

Syllabic (∼2-5 Hz) and fluctuation (∼1-10 Hz) ranges in speech and auditory processing.

Given recent interest in syllabic rates (∼2-5 Hz) for speech processing, we review the perception of "fluctuation" range (∼1-10 Hz) modulations during listening to speech and technical auditory stimuli (AM and FM tones and noises, and ripple sounds). We find evidence that the temporal modulation transfer function (TMTF) of human auditory perception is not simply low-pass in nature, but rather exhibits a peak in sensitivity in the syllabic range (∼2-5 Hz). We also address human and animal neurophysiological evidence, and argue that this bandpass tuning arises at the thalamocortical level and is more associated with non-primary regions than primary regions of cortex. The bandpass rather than low-pass TMTF has implications for modeling auditory central physiology and speech processing: this implicates temporal contrast rather than simple temporal integration, with contrast enhancement for dynamic stimuli in the fluctuation range. This article is part of a Special Issue entitled "Communication Sounds and the Brain: New Directions and Perspectives".

Cortical spatio-temporal dynamics underlying phonological target detection in humans.

Selective processing of task-relevant stimuli is critical for goal-directed behavior. We used electrocorticography to assess the spatio-temporal dynamics of cortical activation during a simple phonological target detection task, in which subjects press a button when a prespecified target syllable sound is heard. Simultaneous surface potential recordings during this task revealed a highly ordered temporal progression of high gamma (HG, 70-200 Hz) activity across the lateral hemisphere in less than 1 sec. The sequence demonstrated concurrent regional sensory processing of speech syllables in the posterior superior temporal gyrus (STG) and speech motor cortex, and then transitioned to sequential task-dependent processing from prefrontal cortex (PFC), to the final motor response in the hand sensorimotor cortex. STG activation was modestly enhanced for target over nontarget sounds, supporting a selective gain mechanism in early sensory processing, whereas PFC was entirely selective to targets, supporting its role in guiding response behavior. These results reveal that target detection is not a single cognitive event, but rather a process of progressive target selectivity that involves large-scale rapid parallel and serial processing in sensory, cognitive, and motor structures to support goal-directed human behavior.

Comparison of wait times and mortality for idiopathic pulmonary fibrosis patients listed for single or bilateral lung transplantation.

BACKGROUND: Lung transplantation is the one form of solid-organ transplantation in which there is the option for patients to receive one or two organs. Idiopathic pulmonary fibrosis (IPF) candidates can be accommodated by either procedure but the decision about these two options remains controversial. Therefore, we sought to determine whether IPF patients listed for bilateral lung transplantation only had longer wait times and higher mortality on the waiting list than those listed for single lungs only. Patients with chronic obstructive pulmonary disease (COPD) were also analyzed as a comparison group. METHODS: This study was a retrospective analysis of the Organ Procurement and Transplantation Network database of patients with IPF and COPD listed for lung transplantation between May 2005 and December 2007. An analysis of wait times and mortality in this era as well as the pre-lung allocation score (pre-LAS) era of 2002 to 2004 was performed. RESULTS: Of the 1,339 patients with IPF listed for lung transplantation, 31.7% were listed for bilateral lung transplantation only, 41% for single-lung transplantation only and 27.3% for either procedure. Patients listed for the bilateral procedure only were at greater risk of dying on the transplant list (p < 0.003), and were less likely to receive a lung transplant (p < 0.012). No difference in outcomes was seen in the COPD patients. Comparatively, in the pre-LAS era, wait times and mortality on the list for IPF patients were significantly greater for all forms of transplantation. CONCLUSIONS: There has been a significant improvement in wait times and mortality for IPF patients since the inception of the LAS system. Nonetheless, despite the goal of transplant equity, IPF patients listed for bilateral lung transplantation might have a clinically meaningful increased risk of pre-transplant mortality. The choice of procedures therefore needs to be made with careful consideration of patients' survival both pre- and post-transplantation. Evaluation of transplant outcomes should not only be based on post-transplant survival, but should also account for the impact of the choice of procedure.

Spatiotemporal imaging of cortical activation during verb generation and picture naming.

One hundred and fifty years of neurolinguistic research has identified the key structures in the human brain that support language. However, neither the classic neuropsychological approaches introduced by Broca (1861) and Wernicke (1874), nor modern neuroimaging employing PET and fMRI has been able to delineate the temporal flow of language processing in the human brain. We recorded the electrocorticogram (ECoG) from indwelling electrodes over left hemisphere language cortices during two common language tasks, verb generation and picture naming. We observed that the very high frequencies of the ECoG (high-gamma, 70-160 Hz) track language processing with spatial and temporal precision. Serial progression of activations is seen at a larger timescale, showing distinct stages of perception, semantic association/selection, and speech production. Within the areas supporting each of these larger processing stages, parallel (or "incremental") processing is observed. In addition to the traditional posterior vs. anterior localization for speech perception vs. production, we provide novel evidence for the role of premotor cortex in speech perception and of Wernicke's and surrounding cortex in speech production. The data are discussed with regards to current leading models of speech perception and production, and a "dual ventral stream" hybrid of leading speech perception models is given.

Comparison of time-frequency responses and the event-related potential to auditory speech stimuli in human cortex.

We recorded the electrocorticogram directly from the exposed cortical surface of awake neurosurgical patients during the presentation of auditory syllable stimuli. All patients were unanesthetized as part of a language-mapping procedure for subsequent left-hemisphere tumor resection. Time-frequency analyses showed significant high-gamma (gammahigh: 70-160 Hz) responses from the left superior temporal gyrus, but no reliable response from the left inferior frontal gyrus. Alpha suppression (alpha: 7-14 Hz) and event-related potential responses exhibited a more widespread topography. Across electrodes, the alpha suppression from 200 to 450 ms correlated with the preceding (50-200 ms) gammahigh increase. The results are discussed in terms of the different physiological origins of these electrocortical signals.

Localization of neurosurgically implanted electrodes via photograph-MRI-radiograph coregistration.

Intracranial electroencephalography (iEEG) is clinically indicated for medically refractory epilepsy and is a promising approach for developing neural prosthetics. These recordings also provide valuable data for cognitive neuroscience research. Accurate localization of iEEG electrodes is essential for evaluating specific brain regions underlying the electrodes that indicate normal or pathological activity, as well as for relating research findings to neuroimaging and lesion studies. However, electrodes are frequently tucked underneath the edge of a craniotomy, inserted via a burr hole, or placed deep within the brain, where their locations cannot be verified visually or with neuronavigational systems. We show that one existing method, registration of postimplant computed tomography (CT) with preoperative magnetic resonance imaging (MRI), can result in errors exceeding 1cm. We present a novel method for localizing iEEG electrodes using routinely acquired surgical photographs, X-ray radiographs, and magnetic resonance imaging scans. Known control points are used to compute projective transforms that link the different image sets, ultimately allowing hidden electrodes to be localized, in addition to refining the location of manually registered visible electrodes. As the technique does not require any calibration between the different image modalities, it can be applied to existing image databases. The final result is a set of electrode positions on the patient's rendered MRI yielding locations relative to sulcal and gyral landmarks on individual anatomy, as well as MNI coordinates. We demonstrate the results of our method in eight epilepsy patients implanted with electrode grids spanning the left hemisphere.

Five-dimensional neuroimaging: localization of the time-frequency dynamics of cortical activity.

The spatiotemporal dynamics of cortical oscillations across human brain regions remain poorly understood because of a lack of adequately validated methods for reconstructing such activity from noninvasive electrophysiological data. In this paper, we present a novel adaptive spatial filtering algorithm optimized for robust source time-frequency reconstruction from magnetoencephalography (MEG) and electroencephalography (EEG) data. The efficacy of the method is demonstrated with simulated sources and is also applied to real MEG data from a self-paced finger movement task. The algorithm reliably reveals modulations both in the beta band (12-30 Hz) and high gamma band (65-90 Hz) in sensorimotor cortex. The performance is validated by both across-subjects statistical comparisons and by intracranial electrocorticography (ECoG) data from two epilepsy patients. Interestingly, we also reliably observed high frequency activity (30-300 Hz) in the cerebellum, although with variable locations and frequencies across subjects. The proposed algorithm is highly parallelizable and runs efficiently on modern high-performance computing clusters. This method enables the ultimate promise of MEG and EEG for five-dimensional imaging of space, time, and frequency activity in the brain and renders it applicable for widespread studies of human cortical dynamics during cognition.

Spatial localization of cortical time-frequency dynamics.

The spatiotemporal dynamics of cortical oscillations across human brain regions remain poorly understood because of a lack of adequately validated methods for reconstructing such activity from noninvasive electrophysiological data. We present a novel adaptive spatial filtering algorithm optimized for robust source time-frequency reconstruction from magnetoencephalography (MEG) and electroencephalography (EEG) data. The efficacy of the method is demonstrated with real MEG data from a self-paced finger movement task. The algorithm reliably reveals modulations both in the beta band (12-30 Hz) and a high gamma band (65-90 Hz) in sensorimotor cortex. The performance is validated by both across-subjects statistical comparisons and by intracranial electrocorticography (ECoG) data from two epilepsy patients. We also revealed observed high gamma activity in the cerebellum. The proposed algorithm is highly parallelizable and runs efficiently on modern high performance computing clusters. This method enables non-invasive five-dimensional imaging of space, time, and frequency activity in the brain and renders it applicable for widespread studies of human cortical dynamics.

Spatiotemporal dynamics of word processing in the human brain.

We examined the spatiotemporal dynamics of word processing by recording the electrocorticogram (ECoG) from the lateral frontotemporal cortex of neurosurgical patients chronically implanted with subdural electrode grids. Subjects engaged in a target detection task where proper names served as infrequent targets embedded in a stream of task-irrelevant verbs and nonwords. Verbs described actions related to the hand (e.g, throw) or mouth (e.g., blow), while unintelligible nonwords were sounds which matched the verbs in duration, intensity, temporal modulation, and power spectrum. Complex oscillatory dynamics were observed in the delta, theta, alpha, beta, low, and high gamma (HG) bands in response to presentation of all stimulus types. HG activity (80-200 Hz) in the ECoG tracked the spatiotemporal dynamics of word processing and identified a network of cortical structures involved in early word processing. HG was used to determine the relative onset, peak, and offset times of local cortical activation during word processing. Listening to verbs compared to nonwords sequentially activates first the posterior superior temporal gyrus (post-STG), then the middle superior temporal gyrus (mid-STG), followed by the superior temporal sulcus (STS). We also observed strong phase-locking between pairs of electrodes in the theta band, with weaker phase-locking occurring in the delta, alpha, and beta frequency ranges. These results provide details on the first few hundred milliseconds of the spatiotemporal evolution of cortical activity during word processing and provide evidence consistent with the hypothesis that an oscillatory hierarchy coordinates the flow of information between distinct cortical regions during goal-directed behavior.

Phase behavior of symmetric ternary block copolymer-homopolymer blends in thin films and on chemically patterned surfaces.

The phase diagram of symmetric ternary blends of diblock copolymers and homopolymers in thin films was determined as a function of increasing volume fraction of homopolymer (phi(H)) and was similar to that for these materials in the bulk. Blends with compositions in the lamellar region of the diagram (phi(H)< or =0.4) could be directed to assemble into ordered lamellar arrays on chemically striped surfaces if the characteristic blend dimension (L(B)) and the period of the stripes (L(S)) were commensurate such that L(S)=L(B)+/-0.10L(B). Blends with compositions in the microemulsion region of the diagram (phi(H) approximately 0.6) assembled into defect-free lamellar phases on patterned surfaces with L(S)> or =L(B), but formed coexisting lamellar (with period L(S)) and homopolymer-rich phases when L(S)

Directing the self-assembly of nanocrystals beyond colloidal crystallization.

This article gives an overview of recent progress in the self-assembly of nanocrystals. Classic self-assembly of nanocrystals, so-called colloidal crystallization driven by van der Waals interactions, is highlighted first with an emphasis on the recent realization of binary colloidal crystals. Next, new developments in the integration of nanocrystals into clusters based on electrostatic interactions, hydrogen bonding and dipole-dipole interactions are summarized, shedding light on the defined control of the interactions between the nanocrystals. Finally, the fabrication of heterogenous nanocrystals, obtained via either phase selective modification at the water/oil interface or facet-selective crystal growth on non-spherical nanocrystals is discussed. These last materials may provide significant building blocks for mimicking molecular self-assembly.

Role of phospholipase C and diacylglyceride lipase pathway in arachidonic acid release and acetylcholine-induced vascular relaxation in rabbit aorta.

ACh stimulates arachidonic acid (AA) release from membrane phospholipids of vascular endothelial cells (ECs). In rabbit aorta, AA is metabolized through the 15-lipoxygenase pathway to form vasodilatory eicosanoids 15-hydroxy-11,12-epoxyeicosatrienoic acid (HEETA) and 11,12,15-trihydroxyeicosatrienoic acid (THETA). AA is released from phosphatidylcholine (PC) and phosphatidylethanolamine (PE) by phospholipase A2 (PLA2), or from phosphatidylinositol (PI) by phospholipase C (PLC) pathway. The diacylglycerol (DAG) lipase can convert DAG into 2-arachidonoylglycerol from which free AA can be released by monoacylglycerol (MAG) lipase or fatty acid amidohydrolase (FAAH). We used specific inhibitors to determine the involvement of the PLC pathway in ACh-induced AA release. In rabbit aortic rings precontracted by phenylephrine, ACh induced relaxation in the presence of indomethacin and N(omega)-nitro-L-arginine (L-NNA). These relaxations were blocked by the PLC inhibitor U-73122, DAG lipase inhibitor RHC-80267, and MAG lipase/FAAH inhibitor URB-532. Cultured rabbit aortic ECs were labeled with [14C]AA and stimulated with methacholine (10(-5) M). Free [14C]AA was released by methacholine. Methacholine decreased the [14C]AA content of PI, DAG, and MAG fractions but not PC or PE fractions. Methacholine-induced release of [14C]AA was blocked by U-73122, RHC-80267, and URB-532 but not by U-73343, an inactive analog of U-73122. The data suggested that ACh activates PLC, DAG lipase, and MAG lipase pathway to release AA from membrane lipids. This pathway is important in regulating vasodilatory eicosanoid synthesis and vascular relaxation in rabbit aorta.

Directed assembly of cylinder-forming block copolymer films and thermochemically induced cylinder to sphere transition: a hierarchical route to linear arrays of nanodots.

A morphological transition from cylinders to spheres was induced in an asymmetric diblock copolymer, poly(styrene)-block-poly(tert-butyl acrylate) (PS-b-PtBA). The periodic arrays of the poly(tert-butyl acrylate) (PtBA) domains were transformed to the ordered poly(acrylic anhydride) (PAA) spheres via the thermal deprotection of tert-butyl acrylate linkages and the subsequent volume change of the minority block. Coupled with techniques to direct the assembly of cylinder-forming block copolymers, this finding provides new routes to fabricate ordered geometries of nanodot arrays.

High gamma activity in response to deviant auditory stimuli recorded directly from human cortex.

We recorded electrophysiological responses from the left frontal and temporal cortex of awake neurosurgical patients to both repetitive background and rare deviant auditory stimuli. Prominent sensory event-related potentials (ERPs) were recorded from auditory association cortex of the temporal lobe and adjacent regions surrounding the posterior Sylvian fissure. Deviant stimuli generated an additional longer latency mismatch response, maximal at more anterior temporal lobe sites. We found low gamma (30-60 Hz) in auditory association cortex, and we also show the existence of high-frequency oscillations above the traditional gamma range (high gamma, 60-250 Hz). Sensory and mismatch potentials were not reliably observed at frontal recording sites. We suggest that the high gamma oscillations are sensory-induced neocortical ripples, similar in physiological origin to the well-studied ripples of the hippocampus.

Directed assembly of block copolymer blends into nonregular device-oriented structures.

Self-assembly is an effective strategy for the creation of periodic structures at the nanoscale. However, because microelectronic devices use free-form design principles, the insertion point of self-assembling materials into existing nanomanufacturing processes is unclear. We directed ternary blends of diblock copolymers and homopolymers that naturally form periodic arrays to assemble into nonregular device-oriented structures on chemically nanopatterned substrates. Redistribution of homopolymer facilitates the defect-free assembly in locations where the domain dimensions deviate substantially from those formed in the bulk. The ability to pattern nonregular structures using self-assembling materials creates new opportunities for nanoscale manufacturing.