Kiyohide Usami

Intraoperative dorsal language network mapping by using single‐pulse electrical stimulation

The preservation of language function during brain surgery still poses a challenge. No intraoperative methods have been established to monitor the language network reliably. We aimed to establish intraoperative language network monitoring by means of cortico‐cortical evoked potentials (CCEPs). Subjects were six patients with tumors located close to the arcuate fasciculus (AF) in the language‐dominant left hemisphere. Under general anesthesia, the anterior perisylvian language area (AL) was first defined by the CCEP connectivity patterns between the ventrolateral frontal and temporoparietal area, and also by presurgical neuroimaging findings. We then monitored the integrity of the language network by stimulating AL and by recording CCEPs from the posterior perisylvian language area (PL) consecutively during both general anesthesia and awake condition. High‐frequency electrical stimulation (ES) performed during awake craniotomy confirmed language function at AL in all six patients. Despite an amplitude decline (≤32%) in two patients, CCEP monitoring successfully prevented persistent language impairment. After tumor removal, single‐pulse ES was applied to the white matter tract beneath the floor of the removal cavity in five patients, in order to trace its connections into the language cortices. In three patients in whom high‐frequency ES of the white matter produced naming impairment, this “eloquent” subcortical site directly connected AL and PL, judging from the latencies and distributions of cortico‐ and subcortico‐cortical evoked potentials. In conclusion, this study provided the direct evidence that AL, PL, and AF constitute the dorsal language network. Intraoperative CCEP monitoring is clinically useful for evaluating the integrity of the language network. Hum Brain Mapp 35:4345–4361, 2014.

Longitudinal fMRI study of reading in a patient with letter-by-letter reading.

The present study provides a longitudinal fMRI study of reading 7 days after a hemorrhage in the left basal occipito-temporal region when the patient showed letter-by-letter (LBL) reading, and repeated again 50 days after onset, when his LBL reading had resolved. Direct comparison of the two sessions showed that right homologue of the so called visual word form area (VWFA), as well as a network related to language and verbal working memory, such as the bilateral premotor areas, Brocas area and its right homologue, and the left supplementary motor area were more strongly activated when his LBL reading persisted than when he recovered, whereas perilesional activity around the VWFA and the activity of superior part of the left superior parietal lobule were more strongly activated when he recovered than when his LBL reading persisted. These results suggest that dynamic functional reorganization of the brain was caused in the acute phase and that the increased activation of certain areas in the left superior parietal lobule in addition to the VWFA may be related to recovery from LBL reading.

Pre-SMA actively engages in conflict processing in human: a combined study of epicortical ERPs and direct cortical stimulation.

Previous non-invasive studies have proposed that the deeply seated region of the medial frontal cortex engages in conflict processing in humans, but its core region has remained to be elucidated. By means of direct cortical stimulation, which excels other techniques in temporal and spatial resolutions and in the capacity of producing transient, functional impairment even in the deeply located cortices, we attempted to obtain direct evidence that the pre-supplementary motor area (pre-SMA) actively engages in conflict processing. Subject was a patient with right frontal lobe epilepsy who underwent invasive presurgical evaluation with subdural electrodes placed on the medial and lateral frontal cortices. During a conflict task--modified Eriksen flanker task, direct cortical stimulation was delivered time-locked to the task at the inferior part of the medial superior frontal gyrus (inferior medial SFG), the superior part of the medial SFG, and the middle frontal gyrus. By adopting the session of sham stimulation that was employed as a within-block control, event-related potentials (ERPs) were recorded from the medial and lateral frontal cortices. The inferior medial SFG showed a significant ERP difference between trials with more and less conflict, while the other frontal cortices did not. Among the three stimulus sites, only stimulation of the inferior medial SFG significantly prolonged reaction time in trials with more conflict. Anatomically, the inferior medial SFG corresponded with the pre-SMA (Brodmann area 8). It was located 1-2 cm rostral to the vertical anterior commissure line where cortical stimulation elicited arrest of motion (the supplementary negative motor area). Functionally, this area corresponded to the dorso-rostral portion of the activation loci in previous neuroimaging studies focusing on conflict processing. By combining epicortical ERP recording and direct cortical stimulation in a human brain, this study, for the first time, presented one direct piece of evidence that the pre-SMA actively participates in conflict processing.

Successful Treatment of Plasma Exchange for Severe Cerebral Venous Thrombosis with Thyrotoxicosis

Although cerebral venous thrombosis (CVT) is generally treated with anticoagulants, some patients have a poor prognosis. We report a 34-year-old woman who developed severe CVT with mental symptoms and intracerebral hemorrhage with central herniation. She had a hypercoagulable state accompanied by thyrotoxicosis. Aggressive medical therapies including unfractionated heparin, a mixture of concentrated glycerin and fructose, and intravenous administration of thiamazole, iohexol, and propranolol were ineffective. The patient was treated with plasma exchange (PE) two times, in addition to aggressive medical therapies. The neurologic symptoms and laboratory data including high levels of thyroid hormones began to improve soon after the first PE. Activated partial thromboplastin time was prolonged after PE although the heparin dose was not changed. After 6 months, her modified Rankin Scale score was 2. PE should be considered for severe CVT as a result of a hypercoagulable state accompanied by thyrotoxicosis, because it not only reduces thyroid hormones, but also might remove multiple prothrombotic factors.

Prolonged ictal monoparesis with parietal Periodic Lateralised Epileptiform Discharges (PLEDs)

We report a patient with prolonged monoparesis and parietal periodic lateralised epileptiform discharges (PLEDs). The patient was a 73-year-old man with chronic myelomonocytic leukaemia who developed persisting monoparesis of the right arm, sensory aphasia, and finger agnosia, initially associated with focal clonic seizures. These neurological deficits remained for seven days without subsequent focal clonic seizures. The EEG showed left-sided PLEDs, maximal in the left occipito-parietal area. Ten days later, following phenytoin treatment, these symptoms suddenly improved and parietal PLEDs disappeared. Sustained PLEDs in the left parietal region may have been causally associated with ictal paresis in this patient.

Different Mode of Afferents Determines the Frequency Range of High Frequency Activities in the Human Brain: Direct Electrocorticographic Comparison between Peripheral Nerve and Direct Cortical Stimulation.

Physiological high frequency activities (HFA) are related to various brain functions. Factors, however, regulating its frequency have not been well elucidated in humans. To validate the hypothesis that different propagation modes (thalamo-cortical vs. cortico-coritcal projections), or different terminal layers (layer IV vs. layer II/III) affect its frequency, we, in the primary somatosensory cortex (SI), compared HFAs induced by median nerve stimulation with those induced by electrical stimulation of the cortex connecting to SI. We employed 6 patients who underwent chronic subdural electrode implantation for presurgical evaluation. We evaluated the HFA power values in reference to the baseline overriding N20 (earliest cortical response) and N80 (late response) of somatosensory evoked potentials (HFASEP(N20) and HFASEP(N80)) and compared those overriding N1 and N2 (first and second responses) of cortico-cortical evoked potentials (HFACCEP(N1) and HFACCEP(N2)). HFASEP(N20) showed the power peak in the frequency above 200 Hz, while HFACCEP(N1) had its power peak in the frequency below 200 Hz. Different propagation modes and/or different terminal layers seemed to determine HFA frequency. Since HFACCEP(N1) and HFA induced during various brain functions share a similar broadband profile of the power spectrum, cortico-coritcal horizontal propagation seems to represent common mode of neural transmission for processing these functions.

Neural pattern similarity between contra- and ipsilateral movements in high-frequency band of human electrocorticograms.

ABSTRACT The cortical motor areas are activated not only during contralateral limb movements but also during ipsilateral limb movements. Although these ipsilateral activities have been observed in several brain imaging studies, their functional role is poorly understood. Due to its high temporal resolution and low susceptibility to artifacts from body movements, the electrocorticogram (ECoG) is an advantageous measurement method for assessing the human brain function of motor behaviors. Here, we demonstrate that contra‐ and ipsilateral movements share a similarity in the high‐frequency band of human ECoG signals. The ECoG signals were measured from the unilateral sensorimotor cortex while patients conducted self‐paced movements of different body parts, contra‐ or ipsilateral to the measurement side. The movement categories (wrist, shoulder, or ankle) of ipsilateral movements were decoded as accurately as those of contralateral movements from spatial patterns of the high‐frequency band of the precentral motor area (the primary motor and premotor areas). The decoder, trained in the high‐frequency band of ipsilateral movements generalized to contralateral movements, and vice versa, confirmed that the activity patterns related to ipsilateral limb movements were similar to contralateral ones in the precentral motor area. Our results suggest that the high‐frequency band activity patterns of ipsilateral and contralateral movements might be functionally coupled to control limbs, even during unilateral movements. HIGHLIGHTSIpsilateral movements can be decoded from the high‐frequency band of ECoG.The decoder is generalized across ipsi‐ and contralateral movements.Similar activity patterns arise in both ipsi‐ and contralateral movements.

Epileptic network of hypothalamic hamartoma: An EEG-fMRI study

OBJECTIVE To investigate the brain networks involved in epileptogenesis/encephalopathy associated with hypothalamic hamartoma (HH) by EEG with functional MRI (EEG-fMRI), and evaluate its efficacy in locating the HH interface in comparison with subtraction ictal SPECT coregistered to MRI (SISCOM). METHODS Eight HH patients underwent EEG-fMRI. All had gelastic seizures (GS) and 7 developed other seizure types. Using a general linear model, spike-related activation/deactivation was analyzed individually by applying a hemodynamic response function before, at, and after spike onset (time-shift model=-8-+4s). Group analysis was also performed. The sensitivity of EEG-fMRI in identifying the HH interface was compared with SISCOM in HH patients having unilateral hypothalamic attachment. RESULTS EEG-fMRI revealed activation and/or deactivation in subcortical structures and neocortices in all patients. 6/8 patients showed activation in or around the hypothalamus with the HH interface with time-shift model before spike onset. Group analysis showed common activation in the ipsilateral hypothalamus, brainstem tegmentum, and contralateral cerebellum. Deactivation occurred in the default mode network (DMN) and bilateral hippocampi. Among 5 patients with unilateral hypothalamic attachment, activation in or around the ipsilateral hypothalamus was seen in 3 using EEG-fMRI, whereas hyperperfusion was seen in 1 by SISCOM. SIGNIFICANCE Group analysis of this preliminary study may suggest that the commonly activated subcortical network is related to generation of GS and that frequent spikes lead to deactivation of the DMN and hippocampi, and eventually to a form of epileptic encephalopathy. Inter-individual variance in neocortex activation explains various seizure types among patients. EEG-fMRI enhances sensitivity in detecting the HH interface compared with SISCOM.

An fMRI Study of Word Reading and Colour Recognition in Different Quadrant Fields

This fMRI study analyzed activations for processing of word and colour, which were presented in each of the four quadrants, to investigate anatomical segregation between colour and orientation processing and also to examine the effect of visual stimulus position on brain activations. Main effect of visual category was found in the bilateral extrastriate cortices extending to the left visual word form area (word > colour) and small area of the right ventrolateral prefrontal cortex (colour > word). ROI analysis showed that there was a tendency that V4α, not V4/8, showed a greater response to colours than to words. Main effect of visual fields was found in early visual areas, which showed greater responses to the left than to the right field stimuli and also to the lower than to the upper field stimuli. No significant interactions between visual category and visual fields were found.

Phasic REM Transiently Approaches Wakefulness in the Human Cortex—A Single-Pulse Electrical Stimulation Study

Study Objectives To investigate the changes in cortical neural responses induced by external inputs during phasic rapid eye movement (p‐REM) sleep. Methods Single‐pulse electrical stimulation (SPES) was directly applied to the human cortex during REM sleep through subdural electrodes, in seven patients who underwent invasive presurgical evaluation for intractable partial epilepsy. SPES was applied to parts of the cortex through the subdural electrodes, and induced cortical responses were recorded from adjacent and remote cortical areas. Phase‐locked corticocortical‐evoked potentials (CCEPs) and nonphase‐locked or induced CCEP‐related high gamma activity (CCEP‐HGA, 100‐200 Hz), which are considered proxies for cortical connectivity and cortical excitability, respectively, were compared among wakefulness, p‐REM (within ±2 seconds of significant bursts of REM), and tonic REM (t‐REM) (periphasic REM) periods. Results During REM sleep, SPES elicited a transient increase in CCEP‐HGA, followed by a subsequent decrease or suppression. The HGA suppression during both p‐REM and t‐REM was stronger than during wakefulness. However, its suppression during p‐REM was weaker than during t‐REM. On the other hand, the CCEP waveform did not show any significant difference between the two REM periods. Conclusions Cortical excitability to exogenous input was different between p‐REM and t‐REM. The change of the cortical excitability in p‐REM was directed toward wakefulness, which may produce incomplete short bursts of consciousness, leading to dreams.