Contralateral Frontal Regions Research Articles

Graph Analysis of TMS-EEG Connectivity Reveals Hemispheric Differences following Occipital Stimulation.

(1) Background: Transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) provides a unique opportunity to investigate brain connectivity. However, possible hemispheric asymmetries in signal propagation dynamics following occipital TMS have not been investigated. (2) Methods: Eighteen healthy participants underwent occipital single-pulse TMS at two different EEG sites, corresponding to early visual areas. We used a state-of-the-art Bayesian estimation approach to accurately estimate TMS-evoked potentials (TEPs) from EEG data, which has not been previously used in this context. To capture the rapid dynamics of information flow patterns, we implemented a self-tuning optimized Kalman (STOK) filter in conjunction with the information partial directed coherence (iPDC) measure, enabling us to derive time-varying connectivity matrices. Subsequently, graph analysis was conducted to assess key network properties, providing insight into the overall network organization of the brain network. (3) Results: Our findings revealed distinct lateralized effects on effective brain connectivity and graph networks after TMS stimulation, with left stimulation facilitating enhanced communication between contralateral frontal regions and right stimulation promoting increased intra-hemispheric ipsilateral connectivity, as evidenced by statistical test (p < 0.001). (4) Conclusions: The identified hemispheric differences in terms of connectivity provide novel insights into brain networks involved in visual information processing, revealing the hemispheric specificity of neural responses to occipital stimulation.

Signs of Electro-cortical Disconnection revealed by Hd-EEG in Acute Stroke Patients: a Case Study. (P10-1.010)

<h3>Objective:</h3> To assess electro-cortical disconnection induced by stroke lesions in two patients with Hd-EEG study. <h3>Background:</h3> There are overwhelming evidences that stroke lesions induce local and remote effects beyond the site of the primary anatomical damage. These networks effects have been studied mainly via neuroimaging techniques. However, little is known about the electrocortical disconnection caused by acute stroke. Moreover, the spatial resolution has been limited by the adoption of standard EEG. <h3>Design/Methods:</h3> 128 channels Hd-EEG was recorded in two acute stroke patients (Patient 1 and Patient 2) in awake state. Patient 1 presented with aphasia and neglect in ischemic stroke involving left insula, temporal and parietal lobe. Patient 2 had mild left side paresis with evidence of extensive hypoperfusion and small multiple ischemic infarcts in right ICA occlusion. Raw data were pre-processed in MATLAB using AMICA in EEGLAB. Power spectra analysis was performed on delta (1–4 Hz), theta (4–8 Hz), alpha (8–12 Hz) and beta (12–25 Hz) frequencies at whole-brain level and within each hemisphere. Values were then compared between the two hemispheres (lesioned vs not lesioned) using a t-test analysis (p&lt;0.05). <h3>Results:</h3> Patient 1 had not only higher delta and theta power over temporo-parietal and posterior frontal regions but also absence of alpha power over posterior occipital regions. In addition to high delta and theta activity over a broad region including frontal and temporoparietal areas in the hypo-perfused hemisphere, Hd-EEG in Patient 2 showed abnormal delta activity over contralateral frontal regions. <h3>Conclusions:</h3> Our findings point to the presence of electro-cortical disconnection that extends the focal lesion borders. Both patients had either delta activity or loss of alpha power in regions distant from the location of the primary local damage/hypoperfusion that was characterized by slowing. Hd-EEG may reveal network disruption in acute stroke patients in a novel and complementary way compared to neuroimaging. <b>Disclosure:</b> Dr. Monai has nothing to disclose. Miss Sevak has nothing to disclose. The institution of Dr. GJINI has received research support from NIH. The institution of Dr. Struck has received research support from Ceribell. Dr. Boly has nothing to disclose.

Trans-falcine and contralateral sub-frontal electrode placement in pediatric epilepsy surgery: technical note.

Phase II monitoring with intracranial electroencephalography (ICEEG) occasionally requires bilateral placement of subdural (SD) strips, grids, and/or depth electrodes. While phase I monitoring often demonstrates a preponderance of unilateral findings, individual studies (video EEG, single photon emission computed tomography [SPECT], and positron emission tomography [PET]) can suggest or fail to exclude a contralateral epileptogenic onset zone. This study describes previously unreported techniques of trans-falcine and sub-frontal insertion of contralateral SD grids and depth electrodes for phase II monitoring in pediatric epilepsy surgery patients when concern about bilateral abnormalities has been elicited during phase I monitoring. Pediatric patients with medically refractory epilepsy undergoing stage I surgery for phase II monitoring involving sub-frontal and/or trans-falcine insertion of SD grids and/or depth electrodes at the senior author's institution were retrospectively reviewed. Intra-operative technical details of sub-frontal and trans-falcine approaches were studied, while intra-operative complications or events were noted. Operative techniques included gentle subfrontal retraction and elevation of the olfactory tracts (while preserving the relationship between the olfactory bulb and cribriform plate) to insert SD grids across the midline for coverage of the contralateral orbito-frontal regions. Trans-falcine approaches involved accessing the inter-hemispheric space, bipolar cauterization of the anterior falx cerebri below the superior sagittal sinus, and sharp dissection using a blunt elevator and small blade scalpel. The falcine window allowed contralateral SD strip, grid, and depth electrodes to be inserted for coverage of the contralateral frontal regions. The study cohort included seven patients undergoing sub-frontal and/or trans-falcine insertion of contralateral SD strip, grid, and/or depth electrodes from February 2012 through June 2015. Five patients (71%) experienced no intra-operative events related to contralateral ICEEG electrode insertion. Intra-operative events of frontal territory venous engorgement (1/7, 14%) due to sacrifice of anterior bridging veins draining into the SSS and avulsion of a contralateral bridging vein (1/7, 14%), probably due to prior anterior corpus callosotomy, each occurred in one patient. There were no intra-operative or peri-operative complications in any of the patients studied. Two patients required additional surgery for supplemental SD strip and/or depth electrodes via burr hole craniectomy to enhance phase II monitoring. All patients proceeded to stage II surgery for resection of ipsilateral epileptogenic onset zones without adverse events. Trans-falcine and sub-frontal insertion of contralateral SD strip, grid, and depth electrodes are previously unreported techniques for achieving bilateral frontal coverage in phase II monitoring in pediatric epilepsy surgery. This technique obviates the need for contralateral craniotomy and parenchymal exposure with limited, remediable risks. Larger case series using the method described herein are now necessary.

Application of envelope trend to analyze early EEG changes in the frontal regions during intracarotid amobarbital procedure in children

BackgroundIntracarotid amobarbital procedure (IAP) is acknowledged as the gold standard test for language lateralization. EEG is performed routinely during IAP to monitor the anesthetization of a brain hemisphere. Here, we studied the correlation between the early EEG changes using envelope trend and the clinical outcome of IAP. MethodFifty consecutive patients underwent IAP at Texas Children's Hospital (2004–2009). Intracarotid amobarbital procedure was considered “complete” or “incomplete” based on the outcome if the procedure was completed or aborted due to behavior changes. Envelope trend was used to calculate the median EEG amplitude changes within the first 60s of IAP. Statistical analysis was performed to determine the role of EEG changes and clinical features on the procedure outcome. ResultsOnly 30 IAP-EEG files were available for review. Amobarbital was administered at the dose of 60–150mg (mean: 110±20). The intracarotid amobarbital procedure was recorded as complete in 23 patients and incomplete in 7 patients. EEG changes occurred within the first few seconds following amobarbital injection. Following amobarbital injection, focal slowing was present in the ipsilateral frontal region or both ipsilateral and contralateral frontal regions. Elapsed time to the first EEG change or duration and change in median EEG amplitude in the ipsilateral frontal regions were indifferent between the complete and incomplete groups (p>0.05). However, the median amplitude changes between the ipsilateral and contralateral frontal regions within each group were found significant only in the complete group (p<0.05), suggesting ipsilateral without contralateral frontal slowing. Other than age at the time of IAP (p=0.03), none of the other clinical features correlated with the clinical outcome of IAP (p>0.05). ConclusionEarly EEG changes during IAP using envelope trend may predict successful completion of the IAP test. Younger children are at risk of behavioral changes during IAP.

Abstract 154: Changes in Task fMRI After Stroke Rehabilitation Using Closed-Loop Neurofeedback

Introduction: Brain-computer interface (BCI) is an emerging technology for stroke rehabilitation, but little is known about brain changes associated with its use. We examine changes in laterality index (LI) and functional connectivity (FC) during hand movements associated with BCI interventional therapy. Methods: We collected anatomical and functional MRI of 8 stroke patients with upper extremity motor impairment before, during, and after up to 6 weeks of therapy using a BCI system with tongue and functional electrical stimulations. We acquired functional images during imagined (MI) and executed (ME) tapping and squeezing of each hand; not all subjects performed all tasks. Two subjects’ scans were flipped so that as a group the lesion was left (L) and the impaired limb right (R). We computed LI using 3 mask sets: whole brain, motor network, and motor cortex. Group-level analyses examined FC changes to motor network seeds using AFNI and Matlab NBS toolbox. Results: BCI intervention led to decreased average LI during tapping. Overall, R taps shifted L to bilateral; all L taps shifted bilateral to R. Trends were consistent across all masks at thresholds p&lt;.05 &amp; p&lt;.001 and were linearly modeled (r2 0.614 to 0.999). During R-ME, FC increased between each thalamus with L M1 and the cingulum. During L-ME, most FC increases were intrahemispheric (R M1 to R thalamus; within L M1). L-ME FC also decreased between each thalamus and contralateral frontal regions and between the cerebellum and frontal lobes. This pattern of inter- and intrahemispheric FC increases during respective R and L movement was also observed with MI, and many FC findings persisted in a subanalysis excluding flipped scans. A network of 6 seeds and 9 edges within the motor network had increased FC during R-ME. All FC changes p&lt;.05. Conclusions: BCI interventional therapy of the impaired hand leads to more bilateral brain activity, while more lateralized activation was seen of the unimpaired hand to its corresponding contralateral motor regions. With different patterns of change observed during tasks using the impaired or unimpaired hand, lesioned brain areas may respond differently to BCI than unlesioned counterparts.

Nasal reconstruction by modified bilobed forehead flap

Paramedian forehead flaps, which are supplied by supratrochlear artery and have structural compatibility with nasal skin, have been successfully used for nasal reconstruction for many years. However, removing this flap from midline as perpendicular to natural lines of forehead may lead to marked scar. A flap extending to lateral in parallel to natural lines of forehead results in ipsilateral elevation of eyebrow. In this article, we aimed to demonstrate a flap technique called as "modified bilobed forehead flap technique". In this technique, pedicle of the flap is supplied by supratrochlear artery at one side and the flap is removed at the contralateral side of the lesion using parallel incision to natural lines of forehead. Another flap with a half thickness of the original flap is removed from contralateral frontal region and interpolated to the site where the original flap is removed to prevent the asymmetrical elevation of eyebrow ipsilateral to flap removal. The aim of this technique is to utilize masking effect of natural lines of forehead, while the basic method is bilobed flap technique. Secondary benefits of this technique include forehead lifting and bilateral eyebrow lifting.

Compensatory Activity in the Aging Brain

Event Abstract Back to Event Compensatory Activity in the Aging Brain Roberto Cabeza1* 1 Duke University, Center for Cognitive Neuroscience, United States Although aging is associated with a significant decline in brain anatomy and function, functional neuroimaging evidence suggests that the aging brain can partially counteract this decline by reorganizing its functions. The talk makes three main points. First, two patterns of brain activity have been consistently observed in multiple cognitive domains and they have been both associated with functional compensation. In the pattern known as Posterior-Anterior Shift with Aging (PASA), older adults show weaker occipital activity but stronger frontal activity than younger adults (Davis, Dennis, Daselaar, Fleck, & Cabeza, 2008). In the pattern known as Hemispheric Asymmetry Reduction in Older adults (HAROLD), older adults display a more bilateral pattern of frontal activity than younger adults (Cabeza, 2002). Three types of evidence link these patterns to functional compensation: (i) a positive association between increased frontal activity and cognitive performance (both PASA and HAROLD), (ii) a negative correlation between increased frontal activity and reduced occipital activity (PASA), and (iii) greater sensitivity of older adults to the disruption of contralateral frontal function (HAROLD). Second, older adults tend display stronger functional connectivity between frontal and posterior regions (c.f. PASA) and between contralateral frontal regions (c.f. HAROLD). These effects have been linked to enhanced cognitive performance and may occur even when frontal activity is weaker in older adults than younger adults. Thus, functional compensation in older may be mediated not only by a local increase in frontal activity but also by an increase in frontal interactions with other brain regions. Third, preliminary evidence suggests that age-related increases in frontal connectivity are modulated by white matter integrity (as measured with diffusion tensor imaging) in specific fiber tracts. For example, connectivity between frontal and medial temporal regions in older adults is modulated by the integrity of the uncinate fasciculus, and connectivity between left and right frontal regions, by the integrity of the genu of the corpus callosum. These findings suggest boundaries to functional compensation in older adults and highlight the importance of linking the effects of aging on brain activity to its effects on brain structure. From an applied perspective, understanding the mechanisms of compensatory activity in the aging brain and the factors that modulate them is critical for the use of functional neuroimaging as an aid in the diagnosis of Alzheimer's disease and in the development and evaluation of cognitive rehabilitation approaches.

Voxel‐based T2 Relaxation Rate Measurements in Temporal Lobe Epilepsy (TLE) with and without Mesial Temporal Sclerosis

Quantitative measurements of T(2) relaxation in the hippocampus for focus lateralization in mesial temporal lobe epilepsy (mTLE) are well established. Less is known to what degree such relaxation abnormalities also affect regions beyond the ipsilateral hippocampus. Therefore, the aim of this study was to characterize extent and distribution pattern of extrahippocampal relaxation abnormalities in TLE with (TLE-MTS) and without MRI evidence of mesial-temporal sclerosis (TLE-no). Double spin echo images (TE1/2: 20/80 ms) acquired in 24 TLE-MTS and 18 TLE-no were used to calculate relaxation rate maps. These maps were analyzed by SPM2 and by selecting regions of interest (ROI) in the hippocampus and several extrahippocampal brain regions. In TLE-MTS, the results of the SPM and ROI analysis were in good agreement and showed the most severe relaxation rate decreases in the ipsilateral hippocampus but also in other ipsilateral temporal regions, orbitofrontal, and parietal regions and to a lesser degree in contralateral frontal regions. The relaxation rate decreases in TLE-no were confined to small regions in the ipsilateral anterior inferior and medial temporal lobe in the SPM analysis while ROI analysis showed additional regions in the ipsilateral hippocampus, amygdala, and anterior cingulate. TLE-MTS showed extensive, widespread but predominantly ipsilateral temporal and also extratemporal T(2) relaxation rate decreases. In contrast, the findings of the SPM and ROI analyses in TLE-no suggested that if relaxation rate decreases are present, they are less uniform and generally milder than in TLE-MTS. This further supports the hypothesis that TLE-no is a distinct clinicopathological entity from TLE-MTS and probably heterogeneous in itself.

Topographic Analysis of Flash Visual Evoked Potentials in Dogs

Visual evoked potentials by flash stimulation (flash VEP) were analyzed in dogs using a topographic method. The flash VEP consisted of 3 positive (P1, P2 and P3) and 2 negative (N1 and N2) components by 150 msec after the flash stimuli. On the topographic mappings, a negative response area was observed in the frontal region of the scalp in the stimulated site followed by the shifting of the area to the contralateral frontal region and occipital region, during the first 100 msec. The negative response area in the frontal region in the stimulated site, contralateral frontal and temporal region, and occipital region were corresponded to N1, P2, and N2 on the flash VEP, respectively, according to their latencies. In the dogs with experimentally impaired the right lateral geniculate body, the latency of P2 was prolonged, and N2 and P3 were disappeared after the left eye stimulation. On the topographic mapping, only the early negative response area was detected on the stimulated site of the frontal region of the brain. Therefore, it is concluded that P1 and N1, P2, and N2 are referred to the retinal potentials, the potentials from the retina to the brainstem included the lateral geniculate body, and those from the brainstem to the visual cortex, respectively.

Paresia poscrítica durante estudios de monitorización de vídeo­EEG

To know the frequency of Todd s paralysis during the video EEG monitoring studies, to investigate in its pathophysiology, and to confirm its value to localise the epileptic focus. We reviewed 114 monitoring studies, in 102 patients. Sixty patients had epileptic seizures. An obvious paresis was noted in four seizures of two patients (3 and 1, respectively). Both patients had frontal epilepsy. During the paralysis, in the first patient the EEG showed ictal discharges on the contralateral centrotemporal area. In the second patient, the EEG demonstrated slow waves in the contralateral frontal region. The ictal onset was contralateral to the paresis in all cases. No patient with pseudoseizures had paralysis. Postconvulsive paralysis are not frequent in video EEG monitoring studies. However, if present it points out to a contralateral seizure onset. In our series it happened in patients with frontal seizures. The EEG may help to clarify if it correspond to a true postictal phenomenon or to a ictal paralysis.

Reconstrucción de la región ciliar mediante colgajo de deslizamiento en V-T

Abstract—The eyebrow and upper eyebrow regions are frequent locations for tumoral lesions whose surgical correction can be troublesome. Reconstruction after tumor excision must be performed without anatomical distortion, avoiding brow elevation, contralateral frontal region asymmetry and, if possible, hair follicle loss.We describe the case of a 72 year old woman who presented a medium size squamous cell carcinoma located on the left eyebrow and upper brow region. After tumor excision, a V-T advancement flap was employed to correct the resultant defect, with both functional and cosmetic satisfactory outcomes.We fulfill the description of this technique and review the different reconstruction possibilities after oncologic surgery of the eyebrow region.

Cortical potentials at the frequency of absolute wrist velocity become phase-locked during slow sinusoidal tracking movements.

A 1-Hz rhythmic event-related potential was recorded at the scalp during performance of a 0.5-Hz tracking task. At cortical motor areas, negative peaks occurred 10-20 ms after peak tracking speeds. Analysis of single sweeps suggested that EEG phase was reset at initiation of the tracking motion and then maintained a constant relationship to wrist speed until task completion. Frequency analysis indicated that rhythm appearance in the averaged potential was predominantly due to phase-locking, because there was no tracking-related increase in 1 Hz amplitude within individual sweeps. While tracking, phase-locking was present over bilateral parieto-occipital and frontal regions, with a slight predominance at the contralateral frontal region. When subjects observed the target motion, phase-locking was localized to parieto-occipital regions. We suggest mental processes such as visual processing, visuomotor coordination and real-time motor planning are reflected in the pacing of localized cortical potential fluctuations.

Contralateral Epidural Hematoma after Aneurysmal Clipping

Cerebral angiograms of a 48-year-old woman with subarachnoid hemorrhage revealed an aneurysm on the anterior communicating artery. The aneurysm was clipped 38 days after onset via the pterional approach, with the patient in the supine position. During surgery, 900 ml of mannitol was administered and her blood pressure and body temperature were normal. However, 1 hour postoperatively, disturbance of consciousness and right hemiparesis were noted. Computed tomographic scans obtained 30 minutes later showed a large epidural hematoma in the left frontoparietal region, contralateral to the craniotomy site. Emergency evacuation of the hematoma was performed. The patient's postoperative course was uneventful and she had fully recovered at the time of discharge. Postoperative epidural hematomas distant to the operative site are often seen after ventricular drainage, shunting, and suboccipital craniectomy and are attributed to intensive internal decompression. However, a review of the literature yielded only four other cases of contralateral epidural hematoma following aneurysmal clipping. Among the five reported cases (the authors' case included), surgery was performed within 16 to 47 days of the onset of subarachnoid hemorrhage. The interval between surgery and detection of the hematoma ranged from 1.5 to 4 hours in four cases. In three cases the hematoma was in the contralateral frontal region.

Conjugate eye deviation after acute hemispheric stroke: delayed recovery after previous contralateral frontal lobe damage.

In 42 patients with acute unilateral ischemic or hemorrhagic hemispheric stroke, conjugate eye deviation toward the lesioned side was usually of brief duration. It subsided within 48 hours in 24 patients (57%) and lasted no longer than 5 days in 38 patients (90%). Early disappearance of conjugate eye deviation was an isolated phenomenon and preceded any improvement in the other focal neurological deficits, which persisted in their initial severity. In 6 additional patients with stroke, conjugate eye deviation was remarkably prolonged, lasting from 13 to more than 43 days. In all 6 there was evidence for preexisting damage to the contralateral frontal region. Our study suggests that early recovery of conjugate eye deviation in patients with acute hemispheric stroke may be mediated by the contralateral unaffected frontal eye field.

Components of the movement-related cortical potential and their scalp topography

In order to clarify the significance of the various components of the movement-related cortical potentials, scalp-recorded potential changes associated with voluntary, self-paced middle finger flexion and extension were studied by an opisthochronic averaging program in 14 normal right-handed subjects. Topographical study, based on 14 simultaneously recorded and averaged EEG channels, enabled us to identify at least 8 components; 4 pre-motion and 4 post-motion. The pre-motion components are the Bereitschaftspotential (BP) (a symmetric early negative shift), NS′(−500 to −90) (a negative slope maximal over the contralateral precentral region and culminating in N−90 ipsilaterally), P−50 (corresponding to the pre-motion positivity, PMP), and N−10 (probably corresponding to the motor potential, MP). The post-motion components include N+50 (a sharp negative post-motion activity over the contralateral frontal region), P+90 , and N+160 (presumably representing sensory functions) and P+300 (a large positivity maximal over the contralateral precentral region but widely distributed).