A visual cortical prosthesis (VCP) has long been proposed as a strategy for restoring useful vision to the blind, under the assumption that visual percepts of small spots of light produced with ...electrical stimulation of visual cortex (phosphenes) will combine into coherent percepts of visual forms, like pixels on a video screen. We tested an alternative strategy in which shapes were traced on the surface of visual cortex by stimulating electrodes in dynamic sequence. In both sighted and blind participants, dynamic stimulation enabled accurate recognition of letter shapes predicted by the brain’s spatial map of the visual world. Forms were presented and recognized rapidly by blind participants, up to 86 forms per minute. These findings demonstrate that a brain prosthetic can produce coherent percepts of visual forms.
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•Visual cortical prosthetic stimulation paradigms were examined•Letters or other shapes were traced on the surface of cortex with electrical current•Static stimulation was unable to produce letter percepts in participants•Dynamic current steering evoked percepts of letter forms by blind and sighted participants
Dynamic stimulation of visual cortex allows both sighted and blind subjects to recognize a variety of letter shapes without training and with high accuracy.
Meningiomas account for one-third of all primary brain tumors. Although typically benign, about 20% of meningiomas are aggressive, and despite the rigor of the current histopathological ...classification system there remains considerable uncertainty in predicting tumor behavior. Here, we analyzed 160 tumors from all 3 World Health Organization (WHO) grades (I through III) using clinical, gene expression, and sequencing data. Unsupervised clustering analysis identified 3 molecular types (A, B, and C) that reliably predicted recurrence. These groups did not directly correlate with the WHO grading system, which classifies more than half of the tumors in the most aggressive molecular type as benign. Transcriptional and biochemical analyses revealed that aggressive meningiomas involve loss of the repressor function of the DREAM complex, which results in cell-cycle activation; only tumors in this category tend to recur after full resection. These findings should improve our ability to predict recurrence and develop targeted treatments for these clinically challenging tumors.
Abstract
BACKGROUND
Delayed hyponatremia is a common complication following transsphenoidal surgery (TSS) of pituitary lesions, which leads to significant patient morbidity, as well as increased ...hospital costs associated with readmission.
OBJECTIVE
To report the effects of fluid restriction, during a postoperative period of 4 d, to decrease rates and readmissions for hyponatremia in a cohort of patients undergoing TSS.
METHODS
Because of our observed postoperative rates of hyponatremia, we implemented 1000-mL fluid restriction limited to postoperative days (POD) 4 to 8 in consecutive patients undergoing surgery at our center between March 2018 and January 2019. Patients were monitored for the development of hyponatremia and readmissions. We compared outcomes with those of patients who had undergone TSS prior to fluid restriction.
RESULTS
Data from 57 patients who underwent TSS following implementation of fluid restriction were compared to prior patients who underwent TSS without restriction. The rate of hyponatremia in patients (n = 57) prior to fluid restriction was 12.3%. Following implementation of fluid restriction, we had zero cases of hyponatremia or readmissions. We found body mass index to be inversely related to the risk of hyponatremia and readmissions. Furthermore, male gender, follicle stimulating hormone and/or luteinizing hormone staining on pathology, and administration of preoperative and intraoperative glucocorticoids were associated with decreased risk of hyponatremia readmissions.
CONCLUSION
The implementation of 1000-mL fluid restriction between POD 4 and 8 is a highly successful and simple approach to decrease the risk of delayed hyponatremia after TSS.
Neocortical gamma activity has long been hypothesized as a mechanism for synchronizing brain regions to support visual perception and cognition more broadly. Although early studies focused on ...narrowband gamma oscillations (∼20–60 Hz), recent work has emphasized a more broadband “high-gamma” response (∼70–150+ Hz). These responses are often conceptually or analytically treated as synonymous markers of gamma activity. Using high-density intracranial recordings from the human visual cortex, we challenge this view by showing distinct spectral, temporal, and functional properties of narrow and broadband gamma. Across four experiments, narrowband gamma was strongly selective for gratings and long-wavelength colors, displaying a delayed response onset, sustained temporal profile, and contrast-dependent peak frequency. In addition, induced narrowband gamma oscillations lacked phase consistency across stimulus repetitions and displayed highly focal inter-site synchronization. In contrast, broadband gamma was consistently observed for all presented stimuli, displaying a rapid response onset, transient temporal profile, and invariant spectral properties. We exploited stimulus tuning to highlight the functional dissociation of these distinct signals, reconciling prior inconsistencies across species and stimuli regarding the ubiquity of visual gamma oscillations during natural vision. The occurrence of visual narrowband gamma oscillations, unlike broadband high gamma, appears contingent on specific structural and chromatic stimulus attributes intersecting with the receptive field. Together, these findings have important implications for the study, analysis, and functional interpretation of neocortical gamma-range activity.
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•Temporal, spectral, and functional properties dissociate narrow and broadband gamma•Narrowband gamma is tuned to visual gratings and long-wavelength hues (red/orange)•Narrowband gamma responses to natural images reflect low-level stimulus tuning•Stimulus dependencies limit the functional role of narrowband gamma oscillations
Gamma oscillations are high-frequency neuro-electrical fluctuations (>20 Hz) proposed to support visual perception. Bartoli et al. use high-density intracranial recordings from the human visual cortex to reveal that gamma oscillations are only induced by specific structural and chromatic stimulus features, limiting their role in visual processing.
During natural speech perception, humans must parse temporally continuous auditory and visual speech signals into sequences of words. However, most studies of speech perception present only single ...words or syllables. We used electrocorticography (subdural electrodes implanted on the brains of epileptic patients) to investigate the neural mechanisms for processing continuous audiovisual speech signals consisting of individual sentences. Using partial correlation analysis, we found that posterior superior temporal gyrus (pSTG) and medial occipital cortex tracked both the auditory and the visual speech envelopes. These same regions, as well as inferior temporal cortex, responded more strongly to a dynamic video of a talking face compared to auditory speech paired with a static face. Occipital cortex and pSTG carry temporal information about both auditory and visual speech dynamics. Visual speech tracking in pSTG may be a mechanism for enhancing perception of degraded auditory speech.
Using partial correlation analysis, we found that neuronal responses in electrodes over posterior superior temporal gyrus (pSTG) and medial occipital cortex tracked, respectively, auditory and visual speech envelopes. In addition, we found a cross‐modal effect of pSTG tracking visual speech while occipital cortex tracks auditory speech envelope. Using magnitude difference between conditions with and without dynamic video, we determined that pSTG is an important location of magnitude modulation.
Human speech can be comprehended using only auditory information from the talker's voice. However, comprehension is improved if the talker's face is visible, especially if the auditory information is ...degraded as occurs in noisy environments or with hearing loss. We explored the neural substrates of audiovisual speech perception using electrocorticography, direct recording of neural activity using electrodes implanted on the cortical surface. We observed a double dissociation in the responses to audiovisual speech with clear and noisy auditory component within the superior temporal gyrus (STG), a region long known to be important for speech perception. Anterior STG showed greater neural activity to audiovisual speech with clear auditory component, whereas posterior STG showed similar or greater neural activity to audiovisual speech in which the speech was replaced with speech-like noise. A distinct border between the two response patterns was observed, demarcated by a landmark corresponding to the posterior margin of Heschl's gyrus. To further investigate the computational roles of both regions, we considered Bayesian models of multisensory integration, which predict that combining the independent sources of information available from different modalities should reduce variability in the neural responses. We tested this prediction by measuring the variability of the neural responses to single audiovisual words. Posterior STG showed smaller variability than anterior STG during presentation of audiovisual speech with noisy auditory component. Taken together, these results suggest that posterior STG but not anterior STG is important for multisensory integration of noisy auditory and visual speech.
High-frequency activity bursts in the hippocampus, known as ripples, are thought to support memory consolidation during “offline” states, such as sleep. Recently, human hippocampal ripples have been ...observed during “online” episodic memory tasks. It remains unclear whether similar ripple activity occurs during other cognitive states, including different types of episodic memory. However, identifying genuine ripple events in the human hippocampus is challenging. To address these questions, spectro-temporal ripple identification was applied to human hippocampal recordings across a variety of cognitive tasks. Overall, ripple attributes were stable across tasks of visual perception and associative memory, with mean rates lower than offline states of rest and sleep. In contrast, while more complex visual attention tasks did not modulate ripple attributes, rates were enhanced for more complex autobiographical memory conditions. Therefore, hippocampal ripples reliably occur across cognitive states but are specifically enhanced during offline states and complex memory processes, consistent with a role in consolidation.
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•Hippocampal ripple detection is improved by time-frequency verification•Ripples occur in human hippocampus during various awake cognitive states at a low rate•Ripple rates are stable across perceptual and associative memory tasks•Ripple rates are enhanced during complex autobiographical memory retrieval
Hippocampal ripples are high-frequency activity bursts proposed to support “offline” memory consolidation. Chen et al. identify that human hippocampal ripples occur with stable properties across tasks of visual perception and associative memory but are enhanced for autobiographical memory retrieval and non-REM sleep, supporting their “online” role in establishing and strengthening memory traces.
Human faces contain multiple sources of information. During speech perception, visual information from the talker's mouth is integrated with auditory information from the talker's voice. By directly ...recording neural responses from small populations of neurons in patients implanted with subdural electrodes, we found enhanced visual cortex responses to speech when auditory speech was absent (rendering visual speech especially relevant). Receptive field mapping demonstrated that this enhancement was specific to regions of the visual cortex with retinotopic representations of the mouth of the talker. Connectivity between frontal cortex and other brain regions was measured with trial-by-trial power correlations. Strong connectivity was observed between frontal cortex and mouth regions of visual cortex; connectivity was weaker between frontal cortex and non-mouth regions of visual cortex or auditory cortex. These results suggest that top-down selection of visual information from the talker's mouth by frontal cortex plays an important role in audiovisual speech perception.
Although humans can understand speech using the auditory modality alone, in noisy environments visual speech information from the talker's mouth can rescue otherwise unintelligible auditory speech. ...To investigate the neural substrates of multisensory speech perception, we compared neural activity from the human superior temporal gyrus (STG) in two datasets. One dataset consisted of direct neural recordings (electrocorticography, ECoG) from surface electrodes implanted in epilepsy patients (this dataset has been previously published). The second dataset consisted of indirect measures of neural activity using blood oxygen level dependent functional magnetic resonance imaging (BOLD fMRI). Both ECoG and fMRI participants viewed the same clear and noisy audiovisual speech stimuli and performed the same speech recognition task. Both techniques demonstrated a sharp functional boundary in the STG, spatially coincident with an anatomical boundary defined by the posterior edge of Heschl's gyrus. Cortex on the anterior side of the boundary responded more strongly to clear audiovisual speech than to noisy audiovisual speech while cortex on the posterior side of the boundary did not. For both ECoG and fMRI measurements, the transition between the functionally distinct regions happened within 10 mm of anterior-to-posterior distance along the STG. We relate this boundary to the multisensory neural code underlying speech perception and propose that it represents an important functional division within the human speech perception network.
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