Satoru Hiroshima

Rapid and Minimum Invasive Functional Brain Mapping by Real-Time Visualization of High Gamma Activity During Awake Craniotomy

BACKGROUND Electrocortical stimulation (ECS) is the gold standard for functional brain mapping during an awake craniotomy. The critical issue is to set aside enough time to identify eloquent cortices by ECS. High gamma activity (HGA) ranging between 80 and 120 Hz on electrocorticogram is assumed to reflect localized cortical processing. In this report, we used real-time HGA mapping and functional neuronavigation integrated with functional magnetic resonance imaging (fMRI) for rapid and reliable identification of motor and language functions. METHODS Four patients with intra-axial tumors in their dominant hemisphere underwent preoperative fMRI and lesion resection with an awake craniotomy. All patients showed significant fMRI activation evoked by motor and language tasks. During the craniotomy, we recorded electrocorticogram activity by placing subdural grids directly on the exposed brain surface. RESULTS Each patient performed motor and language tasks and demonstrated real-time HGA dynamics in hand motor areas and parts of the inferior frontal gyrus. Sensitivity and specificity of HGA mapping were 100% compared with ECS mapping in the frontal lobe, which suggested HGA mapping precisely indicated eloquent cortices. We found different HGA dynamics of language tasks in frontal and temporal regions. Specificities of the motor and language-fMRI did not reach 85%. The results of HGA mapping was mostly consistent with those of ECS mapping, although fMRI tended to overestimate functional areas. CONCLUSIONS This novel technique enables rapid and accurate identification of motor and frontal language areas. Furthermore, real-time HGA mapping sheds light on underlying physiological mechanisms related to human brain functions.

Facephenes and rainbows: Causal evidence for functional and anatomical specificity of face and color processing in the human brain

Significance Are some regions of the human brain exclusively engaged in a single specific mental process? Here we test this question in a neurosurgery patient implanted with electrodes for clinical reasons. When electrically stimulated in the fusiform face area while viewing objects, the patient reported illusory faces while the objects remained unchanged. When stimulated in nearby color-preferring sites, he reported seeing rainbows. The fact that stimulation of face-selective sites affected only face percepts and stimulation of color-preferring sites affected only color percepts, in both cases independent of the object being viewed, supports the view that some regions of cortex are indeed exclusively causally engaged in a single mental process and highlights the risks entailed in standard interpretations of neural decoding results. Neuroscientists have long debated whether some regions of the human brain are exclusively engaged in a single specific mental process. Consistent with this view, fMRI has revealed cortical regions that respond selectively to certain stimulus classes such as faces. However, results from multivoxel pattern analyses (MVPA) challenge this view by demonstrating that category-selective regions often contain information about “nonpreferred” stimulus dimensions. But is this nonpreferred information causally relevant to behavior? Here we report a rare opportunity to test this question in a neurosurgical patient implanted for clinical reasons with strips of electrodes along his fusiform gyri. Broadband gamma electrocorticographic responses in multiple adjacent electrodes showed strong selectivity for faces in a region corresponding to the fusiform face area (FFA), and preferential responses to color in a nearby site, replicating earlier reports. To test the causal role of these regions in the perception of nonpreferred dimensions, we then electrically stimulated individual sites while the patient viewed various objects. When stimulated in the FFA, the patient reported seeing an illusory face (or “facephene”), independent of the object viewed. Similarly, stimulation of color-preferring sites produced illusory “rainbows.” Crucially, the patient reported no change in the object viewed, apart from the facephenes and rainbows apparently superimposed on them. The functional and anatomical specificity of these effects indicate that some cortical regions are exclusively causally engaged in a single specific mental process, and prompt caution about the widespread assumption that any information scientists can decode from the brain is causally relevant to behavior.

Clinical Impact and Implication of Real-Time Oscillation Analysis for Language Mapping

BACKGROUND We developed a functional brain analysis system that enabled us to perform real-time task-related electrocorticography (ECoG) and evaluated its potential in clinical practice. We hypothesized that high gamma activity (HGA) mapping would provide better spatial and temporal resolution with high signal-to-noise ratios. METHODS Seven awake craniotomy patients were evaluated. ECoG was recorded during language tasks using subdural grids, and HGA (60-170 Hz) maps were obtained in real time. The patients also underwent electrocortical stimulation (ECS) mapping to validate the suspected functional locations on HGA mapping. The results were compared and calculated to assess the sensitivity and specificity of HGA mapping. For reference, bedside HGA-ECS mapping was performed in 5 epilepsy patients. RESULTS HGA mapping demonstrated functional brain areas in real time and was comparable with ECS mapping. Sensitivity and specificity for the language area were 90.1% ± 11.2% and 90.0% ± 4.2%, respectively. Most HGA-positive areas were consistent with ECS-positive regions in both groups, and there were no statistical between-group differences. CONCLUSIONS Although this study included a small number of subjects, it showed real-time HGA mapping with the same setting and tasks under different conditions. This study demonstrates the clinical feasibility of real-time HGA mapping. Real-time HGA mapping enabled simple and rapid detection of language functional areas in awake craniotomy. The mapping results were highly accurate, although the mapping environment was noisy. Further studies of HGA mapping may provide the potential to elaborate complex brain functions and networks.

Left hippocampectomy in an epilepsy patient with right hemisphere language dominance

Abstract Background: The left hippocampus is believed to play an important role in memory function. Thus, left hippocampectomy should be carefully performed. However, the left hippocampus may be less important for memory in patients with right hemisphere language dominance. We performed left hippocampectomy in a patient with epilepsy and right hemisphere language dominance. Here we present the findings of our functional mapping and examine the relationship between memory and language dominance. Methods: The patient was a 32-year-old left-handed female implanted with subdural electrocorticography (ECoG) grids over both hemispheres to locate the epilepsy focus. Language dominance was determined by the Wada test. Functional localizations were identified with ECoG and electrocortical stimulation (ECS) mapping. The Wechsler Memory Scale-Revised (WMS-R) was used to evaluate the patient’s memory before and after surgery. Results: The epilepsy focus was located in the left mesial temporal lobe and hippocampus. The Wada test revealed right hemisphere language dominance. High gamma activity (HGA) mapping was consistent with ECS mapping in that both showed language-related activity in the right precentral gyrus. The WMS-R revealed improved memory after left hippocampectomy, without neurological deficits. The patient fully recovered without further epileptic seizures. Conclusion: Left hippocampectomy in a patient with epilepsy and right hemisphere language dominance did not cause memory dysfunction. Thus, memory function is possibly related to the language-dominant hemisphere. Furthermore, preoperative mapping and determining a patient’s language dominance can help to preserve language and memory in epilepsy surgery.

Disconnection of the pathological connectome for multifocal epilepsy surgery

OBJECTIVERecent neuroimaging studies suggest that intractable epilepsy involves pathological functional networks as well as strong epileptogenic foci. Combining cortico-cortical evoked potential (CCEP) recording and tractography is a useful strategy for mapping functional connectivity in normal and pathological networks. In this study, the authors sought to demonstrate the efficacy of preoperative combined CCEP recording, high gamma activity (HGA) mapping, and tractography for surgical planning, and of intraoperative CCEP measures for confirmation of selective pathological network disconnection.METHODSThe authors treated 4 cases of intractable epilepsy. Diffusion tensor imaging-based tractography data were acquired before the first surgery for subdural grid implantation. HGA and CCEP investigations were done after the first surgery, before the second surgery was performed to resect epileptogenic foci, with continuous CCEP monitoring during resection.RESULTSAll 4 patients in this report had measurable pathological CCEPs. The mean negative peak-1 latency of normal CCEPs related to language functions was 22.2 ± 3.5 msec, whereas pathological CCEP latencies varied between 18.1 and 22.4 msec. Pathological CCEPs diminished after complete disconnection in all cases. At last follow-up, all of the patients were in long-term postoperative seizure-free status, although 1 patient still suffered from visual aura every other month.CONCLUSIONSCombined CCEP measurement, HGA mapping, and tractography greatly facilitated targeted disconnection of pathological networks in this study. Although CCEP recording requires technical expertise, it allows for assessment of pathological network involvement in intractable epilepsy and may improve seizure outcome.

A Case of Facial Spasm Associated with Ipsilateral Cerebellopontine Angle Arachnoid Cyst

The authors report a rare case of right cerebellopontine angle cyst related to hemifacial spasm. The patient was a 66-year-old woman with a 3-year history of right hemifacial spasm. The cyst was diagnosed preoperatively by T2-weighted magnetic resonance imaging, which demonstrated a hyperintense area in the right cerebellopontine angle. A small artery was displaced by the cyst and compressed the root exit zone of the facial nerve. Decompression of the cyst and the vasculature using a microsurgical technique resulted in total recovery from hemifacial spasm.