A distributed network supports spatiotemporal cerebral dynamics of visual naming

Chronobiological Spatial Clusters of Cortical Regions in the Human Brain

PURPOSE

We demonstrate that different regions of the cerebral cortex have different diurnal rhythms of spontaneously occurring high-frequency oscillations (HFOs).

METHODS

High-frequency oscillations were assessed with standard-of-care stereotactic electroencephalography in patients with drug-resistant epilepsy. To ensure generalizability of our findings beyond patients with drug-resistant epilepsy, we excluded stereotactic electroencephalography electrode contacts lying within seizure-onset zones, epileptogenic lesions, having frequent epileptiform activity, and excessive artifact. For each patient, we evaluated twenty-four 5-minute stereotactic electroencephalography epochs, sampled hourly throughout the day, and obtained the HFO rate (number of HFOs/minute) in every stereotactic electroencephalography channel. We analyzed diurnal rhythms of the HFO rates with the cosinor model and clustered neuroanatomic parcels in a standard brain space based on similarity of their cosinor parameters. Finally, we compared overlap among resting-state networks, described in the neuroimaging literature, and chronobiological spatial clusters discovered by us.

RESULTS

We found five clusters that localized predominantly or exclusively to the left perisylvian, left perirolandic and left temporal, right perisylvian and right parietal, right frontal, and right insular-opercular cortices, respectively. These clusters were characterized by similarity of the HFO rates according to the time of the day. Also, these chronobiological spatial clusters preferentially overlapped with specific resting-state networks, particularly default mode network (clusters 1 and 3), frontoparietal network (cluster 1), visual network (cluster 1), and mesial temporal network (cluster 2).

CONCLUSIONS

This is probably the first human study to report clusters of cortical regions with similar diurnal rhythms of electrographic activity. Overlap with resting-state networks attests to their functional significance and has implications for understanding cognitive functions and epilepsy-related mortality.

Complex dynamic behavioral transitions in auditory neurons induced by chaotic activity

Chaotic sequences are widely used in secure communication due to their high randomness. Chaotic resonance (CR) refers to the resonant response of a system to weak signals induced by chaotic activity, but its practical application remains limited. This study designs a simplified FitzHugh-Nagumo (FHN) auditory neuron model by simulating the physiological activities of auditory neurons and considering the combined stimulation of chaotic activity and sound signals. It is found that the neuron dynamics depend on both external sound stimuli and chaotic current intensity. Chaotic currents induce spikes in the neuron output sequence through CR, and the spikes become more frequent with increasing current intensity, eventually leading to a chaotic state regardless of the initial state. However, the sensitivity of the initial value of this chaotic sequence shifts to the chaotic current excitation system. The injection of chaotic currents can reduce the system's average Hamiltonian energy under certain conditions. By measuring the complexity of the generated sequences, we find that the addition of chaotic currents can enhance the complexity of the original sequences, and the enhancement ability increases with the intensity. This provides a new approach to enhance the complexity of original chaotic sequences. Moreover, different chaotic currents can induce different chaotic sequences with varying abilities to enhance the complexity of the original sequences. We hope our work can contribute to secure communication.

Bipolar and Laplacian montages are suitable for high-gamma modulation language mapping with stereoelectroencephalography

Objective

To determine the optimal montage and vocalization conditions for high-gamma language mapping using stereoelectroencephalography.

Methods

We studied 12 epilepsy patients who underwent invasive monitoring with depth electrodes and measurement of auditory-naming related high-gamma modulations. We determined the effects of electrode montage and vocalization conditions of the response on the high-gamma (60-140 Hz) amplitudes.

Results

Compared to common average reference montage, bipolar and Laplacian montages effectively reduced the degree of auditory naming-related signal deflections in the white matter during the stimulus and response phases (mixed model estimate: -21.2 to -85.4%; p < 0.001), while maintaining those at the cortical level (-4.4 to +7.8%; p = 0.614 to 0.085). They also reduced signal deflections outside the brain parenchyma during the response phase (-90.6 to -91.2%; p < 0.001). Covert responses reduced signal deflections outside the brain parenchyma during the response phase (-17.0%; p = 0.010).

Conclusion

On depth electrode recording, bipolar and Laplacian montages are suitable for measuring auditory naming-related high-gamma modulations in gray matter. The covert response may highlight the gray matter activity.

Significance

This study helps establish the practical guidelines for high-gamma language mapping using stereoelectroencephalography.

High-gamma modulation language mapping and cognitive outcomes after epilepsy surgery

OBJECTIVE

We evaluated changes in cognitive domains after neurosurgical lesioning of cortical sites with significant high-gamma power modulations (HGM) during a visual naming task, although these sites were found language-negative on standard-of-care electrical stimulation mapping (ESM).

METHODS

In drug-resistant epilepsy patients who underwent resection/ablation after stereo-electroencephalography (SEEG), we computed reliable change indices (RCIs) from a battery of presurgical and 1-year postsurgical neuropsychological assessments. We modeled RCIs as a function of lesioning even one HGM language site, number of HGM language sites lesioned, and the magnitude of naming-related HGM. The analyses were adjusted for 1-year seizure freedom, operated hemispheres, and the volumes of surgical lesions.

RESULTS

In 37 patients with 4455 SEEG electrode contacts (1839 and 2616 contacts in right and left hemispheres, respectively), no ESM language sites were lesioned. Patients with lesioning of even one HGM language site showed significantly lower RCIs for Peabody Picture Vocabulary Test (PPVT), working memory, and verbal learning immediate (VLI) scores. RCI declines with higher number of HGM language sites lesioned were seen in PPVT (slope [β] = -.10), working memory (β = -.10), VLI (β = -.14), and letter-word identification (LWI; β = -.14). No neuropsychological domains improved after lesioning of HGM language sites. Significant effects of the HGM magnitude at lesioned sites were seen on working memory (β = -.31), story memory immediate (β = -.27), verbal learning recognition (β = -.18), LWI (β = -.16), spelling (β = -.49), and passage comprehension (β = -.33). Because working memory was significantly affected in all three analyses, patients with maximal working memory decline were examined post hoc, revealing that all such patients had HGM naming sites lesioned in the posterior quadrants of either hemisphere.

SIGNIFICANCE

HGM language mapping should be used as an adjunct to ESM in clinical practice and may help counsel patients/families about postsurgical cognitive deficits.

The changing landscape of electrical stimulation language mapping with subdural electrodes and stereoelectroencephalography for pediatric epilepsy: A literature review and commentary

Electrical stimulation mapping (ESM) is used to locate the brain areas supporting language directly within the human cortex to minimize the risk of functional decline following epilepsy surgery. ESM is completed by utilizing subdural grid or depth electrodes (stereo-electroencephalography [sEEG]) in combination with behavioral evaluation of language. Despite technological advances, there is no standardized method of assessing language during pediatric ESM. To identify current clinical practices for pediatric ESM of language, we surveyed neuropsychologists in the Pediatric Epilepsy Research Consortium. Results indicated that sEEG is used for functional mapping at >80% of participating epilepsy surgery centers (n = 13/16) in the United States. However, >65% of sites did not report a standardized protocol to map language. Survey results indicated a clear need for practice recommendations regarding ESM of language. We then utilized PubMed/Medline and PsychInfo to identify 42 articles that reported on ESM of language, of which 18 met inclusion criteria, which included use of ESM/signal recording to localize language regions in children (<21 years) and a detailed account of the procedure and language measures used, and region-specific language localization outcomes. Articles were grouped based on the language domain assessed, language measures used, and the brain regions involved. Our review revealed the need for evidence-based clinical guidelines for pediatric language paradigms during ESM and a standardized language mapping protocol as well as standardized reporting of brain regions in research. Relevant limitations and future directions are discussed with a focus on considerations for pediatric language mapping.

Emotional facial expression and perioral motor functions of the human auditory cortex

OBJECTIVE

We investigated the role of transverse temporal gyrus and adjacent cortex (TTG+) in facial expressions and perioral movements.

METHODS

In 31 patients undergoing stereo-electroencephalography monitoring, we describe behavioral responses elicited by electrical stimulation within the TTG+. Task-induced high-gamma modulation (HGM), auditory evoked responses, and resting-state connectivity were used to investigate the cortical sites having different types of responses on electrical stimulation.

RESULTS

Changes in facial expressions and perioral movements were elicited on electrical stimulation within TTG+ in 9 (29%) and 10 (32%) patients, respectively, in addition to the more common language responses (naming interruptions, auditory hallucinations, paraphasic errors). All functional sites showed auditory task induced HGM and evoked responses validating their location within the auditory cortex, however, motor sites showed lower peak amplitudes and longer peak latencies compared to language sites. Significant first-degree connections for motor sites included precentral, anterior cingulate, parahippocampal, and anterior insular gyri, whereas those for language sites included posterior superior temporal, posterior middle temporal, inferior frontal, supramarginal, and angular gyri.

CONCLUSIONS

Multimodal data suggests that TTG+ may participate in auditory-motor integration.

SIGNIFICANCE

TTG+ likely participates in facial expressions in response to emotional cues during an auditory discourse.

Neuropsychological outcomes after epilepsy surgery: A comparison of stereo electroencephalography and subdural electrodes

BACKGROUND AND PURPOSE

We analyzed the association of neuropsychological outcomes after epilepsy surgery with the intracranial electrode type (stereo electroencephalography [SEEG] and subdural electrodes [SDE]), and electrical stimulation mapping (ESM) of speech/language.

METHODS

Drug-resistant epilepsy patients who underwent comprehensive neuropsychological evaluation before and 1 year after epilepsy surgery were included. SEEG and SDE subgroups were matched by age, handedness, operated hemisphere, and seizure freedom. Postsurgical neuropsychological outcomes (adjusted for presurgical scores) and reliable change indices were analyzed as functions of electrode type and ESM.

RESULTS

Ninety-nine patients aged 6-29 years were included with similar surgical resection/ablation volumes in the SEEG and SDE subgroups. Most of the neuropsychological outcomes were comparable between SEEG and SDE subgroups; however, Working Memory and Processing Speed were significantly improved in the SEEG subgroup. Undergoing language ESM was associated with significant improvements in Spelling, Letter-Word Identification, Vocabulary, Verbal Comprehension, Verbal Learning, and Story Memory scores, but a decline in Calculation scores.

CONCLUSIONS

Intracranial evaluations with SEEG and SDE are comparable in terms of long-term postsurgical neuropsychological outcomes. Our data suggest that SEEG may be associated with improvements in working memory and processing speed, representing cognitive domains served by spatially distributed networks. Our study also supports wider use of language ESM before epilepsy surgery, preferably using other language tasks in addition to visual naming. Rather than the type of electrode, postsurgical neuropsychological outcomes are driven by whether language ESM was performed or not, with beneficial effects of language mapping.

Intra- and inter-hemispheric network dynamics supporting object recognition and speech production

We built normative brain atlases that animate millisecond-scale intra- and inter-hemispheric white matter-level connectivity dynamics supporting object recognition and speech production. We quantified electrocorticographic modulations during three naming tasks using event-related high-gamma activity from 1,114 nonepileptogenic intracranial electrodes (i.e., non-lesional areas unaffected by epileptiform discharges). Using this electrocorticography data, we visualized functional connectivity modulations defined as significant naming-related high-gamma modulations occurring simultaneously at two sites connected by direct white matter streamlines on diffusion-weighted imaging tractography. Immediately after stimulus onset, intra- and inter-hemispheric functional connectivity enhancements were confined mainly across modality-specific perceptual regions. During response preparation, left intra-hemispheric connectivity enhancements propagated in a posterior-to-anterior direction, involving the left precentral and prefrontal areas. After overt response onset, inter- and intra-hemispheric connectivity enhancements mainly encompassed precentral, postcentral, and superior-temporal (STG) gyri. We found task-specific connectivity enhancements during response preparation as follows. Picture naming enhanced activity along the left arcuate fasciculus between the inferior-temporal and precentral/posterior inferior-frontal (pIFG) gyri. Nonspeech environmental sound naming augmented functional connectivity via the left inferior longitudinal and fronto-occipital fasciculi between the medial-occipital and STG/pIFG. Auditory descriptive naming task enhanced usage of the left frontal U-fibers, involving the middle-frontal gyrus. Taken together, the commonly observed network enhancements include inter-hemispheric connectivity optimizing perceptual processing exerted in each hemisphere, left intra-hemispheric connectivity supporting semantic and lexical processing, and inter-hemispheric connectivity for symmetric oral movements during overt speech. Our atlases improve the currently available models of object recognition and speech production by adding neural dynamics via direct intra- and inter-hemispheric white matter tracts.

Neuronal Circuits Supporting Development of Visual Naming Revealed by Intracranial Coherence Modulations

Background

Improvement in visual naming abilities throughout the childhood and adolescence supports development of higher-order linguistic skills. We investigated neuronal circuits underlying improvement in the speed of visual naming with age, and age-related dynamics of these circuits.

Methods

Response times were electronically measured during an overt visual naming task in epilepsy patients undergoing stereo-EEG monitoring. Coherence modulations among pairs of neuroanatomic parcels were computed and analyzed for relationship with response time and age.

Results

During the overt visual naming task, mean response time (latency) significantly decreased from 4 to 23 years of age. Coherence modulations during visual naming showed that increased connectivity between certain brain regions, particularly that between left fusiform gyrus/left parahippocampal gyrus and left frontal operculum, is associated with improvement in naming speed. Also, decreased connectivity in other brain regions, particularly between left angular and supramarginal gyri, is associated with decreased mean response time. Further, coherence modulations between left frontal operculum and both left fusiform and left posterior cingulate gyri significantly increase, while that between left angular and supramarginal gyri significantly decrease, with age.

Conclusion

Naming speed continues to improve from pre-school years into young adulthood. This age-related improvement in efficiency of naming environmental objects occurs likely because of strengthened direct connectivity between semantic and phonological nodes, and elimination of intermediate higher-order cognitive steps.