Adeen Flinker

Reconstructing speech from human auditory cortex.

Direct brain recordings from neurosurgical patients listening to speech reveal that the acoustic speech signals can be reconstructed from neural activity in auditory cortex.

Predicting Odor Pleasantness from Odorant Structure: Pleasantness as a Reflection of the Physical World

Although it is agreed that physicochemical features of molecules determine their perceived odor, the rules governing this relationship remain unknown. A significant obstacle to such understanding is the high dimensionality of features describing both percepts and molecules. We applied a statistical method to reduce dimensionality in both odor percepts and physicochemical descriptors for a large set of molecules. We found that the primary axis of perception was odor pleasantness, and critically, that the primary axis of physicochemical properties reflected the primary axis of olfactory perception. This allowed us to predict the pleasantness of novel molecules by their physicochemical properties alone. Olfactory perception is strongly shaped by experience and learning. However, our findings suggest that olfactory pleasantness is also partially innate, corresponding to a natural axis of maximal discriminability among biologically relevant molecules.

Redefining the role of Broca’s area in speech

Significance Broca’s area is widely recognized to be important for speech production, but its specific role in the dynamics of cortical language networks is largely unknown. Using direct cortical recordings of these dynamics during vocal repetition of written and spoken words, we found that Broca’s area mediates a cascade of activation from sensory representations of words in temporal cortex to their corresponding articulatory gestures in motor cortex, but it is surprisingly quiescent during articulation. Contrary to classic notions of this area’s role in speech, our results indicate that Broca’s area does not participate in production of individual words, but coordinates the transformation of information processing across large-scale cortical networks involved in spoken word production, prior to articulation. For over a century neuroscientists have debated the dynamics by which human cortical language networks allow words to be spoken. Although it is widely accepted that Broca’s area in the left inferior frontal gyrus plays an important role in this process, it was not possible, until recently, to detail the timing of its recruitment relative to other language areas, nor how it interacts with these areas during word production. Using direct cortical surface recordings in neurosurgical patients, we studied the evolution of activity in cortical neuronal populations, as well as the Granger causal interactions between them. We found that, during the cued production of words, a temporal cascade of neural activity proceeds from sensory representations of words in temporal cortex to their corresponding articulatory gestures in motor cortex. Broca’s area mediates this cascade through reciprocal interactions with temporal and frontal motor regions. Contrary to classic notions of the role of Broca’s area in speech, while motor cortex is activated during spoken responses, Broca’s area is surprisingly silent. Moreover, when novel strings of articulatory gestures must be produced in response to nonword stimuli, neural activity is enhanced in Broca’s area, but not in motor cortex. These unique data provide evidence that Broca’s area coordinates the transformation of information across large-scale cortical networks involved in spoken word production. In this role, Broca’s area formulates an appropriate articulatory code to be implemented by motor cortex.

Single-Trial Speech Suppression of Auditory Cortex Activity in Humans

The human auditory cortex is engaged in monitoring the speech of interlocutors as well as self-generated speech. During vocalization, auditory cortex activity is reported to be suppressed, an effect often attributed to the influence of an efference copy from motor cortex. Single-unit studies in non-human primates have demonstrated a rich dynamic range of single-trial auditory responses to self-speech consisting of suppressed, nonsuppressed and excited auditory neurons. However, human research using noninvasive methods has only reported suppression of averaged auditory cortex responses to self-generated speech. We addressed this discrepancy by recording electrocorticographic activity from neurosurgical subjects performing auditory repetition tasks. We observed that the degree of suppression varied across different regions of auditory cortex, revealing a variety of suppressed and nonsuppressed responses during vocalization. Importantly, single-trial high-gamma power (γHigh, 70–150 Hz) robustly tracked individual auditory events and exhibited stable responses across trials for suppressed and nonsuppressed regions.

Sub-centimeter language organization in the human temporal lobe.

The human temporal lobe is well known to be critical for language comprehension. Previous physiological research has focused mainly on non-invasive neuroimaging and electrophysiological techniques with each approach requiring averaging across many trials and subjects. The results of these studies have implicated extended anatomical regions in peri-sylvian cortex in speech perception. These non-invasive studies typically report a spatially homogenous functional pattern of activity across several centimeters of cortex. We examined the spatiotemporal dynamics of word processing using electrophysiological signals acquired from high-density electrode arrays (4mm spacing) placed directly on the human temporal lobe. Electrocorticographic (ECoG) activity revealed a rich mosaic of language activity, which was functionally distinct at four mm separation. Cortical sites responding specifically to word and not phoneme stimuli were surrounded by sites that responded to both words and phonemes. Other sub-regions of the temporal lobe responded robustly to self-produced speech and minimally to external stimuli while surrounding sites at 4mm distance exhibited an inverse pattern of activation. These data provide evidence for temporal lobe specificity to words as well as self-produced speech. Furthermore, the results provide evidence that cortical processing in the temporal lobe is not spatially homogenous over centimeters of cortex. Rather, language processing is supported by independent and spatially distinct functional sub-regions of cortex at a resolution of at least 4mm.

Spatial-temporal functional mapping of language at the bedside with electrocorticography

Objective: To investigate the feasibility and clinical utility of using passive electrocorticography (ECoG) for online spatial-temporal functional mapping (STFM) of language cortex in patients being monitored for epilepsy surgery. Methods: We developed and tested an online system that exploits ECoGs temporal resolution to display the evolution of statistically significant high gamma (70–110 Hz) responses across all recording sites activated by a discrete cognitive task. We illustrate how this spatial-temporal evolution can be used to study the function of individual recording sites engaged during different language tasks, and how this approach can be particularly useful for mapping eloquent cortex. Results: Using electrocortical stimulation mapping (ESM) as the clinical gold standard for localizing language cortex, the average sensitivity and specificity of online STFM across 7 patients were 69.9% and 83.5%, respectively. Moreover, relative to regions of interest where discrete cortical lesions have most reliably caused language impairments in the literature, the sensitivity of STFM was significantly greater than that of ESM, while its specificity was also greater than that of ESM, though not significantly so. Conclusions: This study supports the feasibility and clinical utility of online STFM for mapping human language function, particularly under clinical circumstances in which time is limited and comprehensive ESM is impractical.

Differential sources for 2 neural signatures of target detection: An electrocorticography study

Electrophysiology and neuroimaging provide conflicting evidence for the neural contributions to target detection. Scalp electroencephalography (EEG) studies localize the P3b event-related potential component mainly to parietal cortex, whereas neuroimaging studies report activations in both frontal and parietal cortices. We addressed this discrepancy by examining the sources that generate the target-detection process using electrocorticography (ECoG). We recorded ECoG activity from cortex in 14 patients undergoing epilepsy monitoring, as they performed an auditory or visual target-detection task. We examined target-related responses in 2 domains: high frequency band (HFB) activity and the P3b. Across tasks, we observed a greater proportion of electrodes that showed target-specific HFB power relative to P3b over frontal cortex, but their proportions over parietal cortex were comparable. Notably, there was minimal overlap in the electrodes that showed target-specific HFB and P3b activity. These results revealed that the target-detection process is characterized by at least 2 different neural markers with distinct cortical distributions. Our findings suggest that separate neural mechanisms are driving the differential patterns of activity observed in scalp EEG and neuroimaging studies, with the P3b reflecting EEG findings and HFB activity reflecting neuroimaging findings, highlighting the notion that target detection is not a unitary phenomenon.

Hippocampal signature of associative memory measured by chronic ambulatory intracranial EEG

Some patients with medically refractory focal epilepsy are chronically implanted with a brain-responsive neurostimulation device (the RNS® System), permitting neurophysiological measurements at millisecond resolution. This clinical device can be adapted to measure hippocampal dynamics time-locked to cognitive tasks. We illustrate the technique with a proof of concept in three patients previously implanted with the RNS System as they engage in an associative memory task, measured months apart. Hippocampal activity measured in successful encoding in RNS System patients mirrors that in surgical patients during intracranial electroencephalography (iEEG), suggesting that chronic iEEG allows sensitive measurements of hippocampal physiology over prolonged timescales.

T104. Neural correlates of sign language and spoken language revealed by electrocorticography

Introduction Electrocorticography (ECoG) is a powerful tool to monitor cortical neurophysiology and can be employed to elucidate high order cognitive functions such as language. Clinically, electrical stimulation mapping (ESM) is the gold standard used to identify eloquent cortex which should be spared resection during surgery for patients. We developed a battery of tasks that mirror the ESM paradigm but can functionally track neural activity from stimulus presentation through speech output under multiple cognitive demands. Here we describe the neural propagation maps during both speech and sign language output in a case of a 28 year old male, hearing intact and bilingual in English and American sign language, with pharmaco-resistant epilepsy who was surgically implanted with electrodes for the clinical purpose of identifying his seizure onset zones. Methods The patient was implanted, for the purposes of his clinical care, with an electrode grid over the left temporal parietal occipital cortex, strips over the left frontal, temporal, and occipital regions, and depths within the left parietal lobe. During lulls in clinical treatment, we administered five language tasks involving visual naming, word reading, auditory repetition, auditory naming, and auditory comprehension. We focused our analyses on changes in high gamma activity (70–150 Hz) during the tasks, as high gamma activation has been previously shown to robustly track single trial cortical activity and correlates with neural population firing rates and fMRI BOLD responses. The patient also underwent electrical stimulation mapping using similar language tasks of visual naming, auditory naming, and auditory comprehension, as part of his clinical work up to identify eloquent cortex. Results We identified brain regions with high gamma activation during our language tasks in both spoken English and sign language. In addition we identified discrete regions in the frontal, temporal, parietal, and occipital cortices with sign language specific responses compared to spoken English and provide evidence for temporal propagation of neural activity from post-central to occipital cortices during sign language production. Conclusion We used ECoG high gamma activity to track neural dynamics of language processing in both spoken English and American sign language and to help map language cortex to assist in identifying eloquent regions during electrical brain stimulation.

A Cool Approach to Probing Speech Cortex

In this issue of Neuron, Long et al. (2016) employ a novel technique of intraoperative cortical cooling in humans during speech production. They demonstrate that cooling Brocas area interferes with speech timing but not speech quality.