Spatiotemporal dynamics and functional correlates of evoked neural oscillations with different spectral powers in human visual cortex

Objective

To investigate spatiotemporal characteristics and functional correlates of evoked oscillations (EOs) at different frequency bands in human visual cortex.

Methods

Flash visual evoked potentials (FVEPs) were recorded from 11 epilepsy patients with intracranial electrodes placed over the occipital and adjacent cortices. Spatiotemporal characteristics of spectral powers and correlation with various visual responses elicited by electrical cortical stimulations were analyzed in the same electrodes.

Results

High γ (60–150 Hz) EOs were first recorded in the cuneus and lingual gyri around the calcarine sulcus. Low γ (30–60 Hz) EOs appeared also in the mesial occipital cortex slightly later and lasted longer than high γ EGOs. In contrast, lower frequency (LF) <30 Hz EOs were recorded more diffusely from occipital surfaces with delayed onset and longer duration. High γ EOs were predominantly associated with simple form visual responses, whereas low γ and LF EOs were with intermediate form and LF EOs with complex form responses.

Conclusions

FVEP spectral power analysis directly recorded from human visual cortex showed distinct spatiotemporal distributions in high and low γ, or LF bands that have different functional correlates.

Significance

Phase-locked EOs in these frequency bands may have special neuroanatomical and functional organization during early visual processing.     

Clinical Utility of Interictal High-Frequency Oscillations Recorded with Subdural Macroelectrodes in Partial Epilepsy

Background and Purpose

There is growing interest in high-frequency oscillations (HFO) as electrophysiological biomarkers of the epileptic brain. We evaluated the clinical utility of interictal HFO events, especially their occurrence rates, by comparing the spatial distribution with a clinically determined epileptogenic zone by using subdural macroelectrodes.

Methods

We obtained intracranial electroencephalogram data with a high temporal resolution (2000 Hz sampling rate, 0.05-500 Hz band-pass filter) from seven patients with medically refractory epilepsy. Three epochs of 5-minute, artifact-free data were selected randomly from the interictal period. HFO candidates were first detected by an automated algorithm and subsequently screened to discard false detections. Validated events were further categorized as fast ripple (FR) and ripple (R) according to their spectral profiles. The occurrence rate of HFOs was calculated for each electrode contact. An HFO events distribution map (EDM) was constructed for each patient to allow visualization of the spatial distribution of their HFO events.

Results

The subdural macroelectrodes were capable of detecting both R and FR events from the epileptic neocortex. The occurrence rate of HFO events, both FR and R, was significantly higher in the seizure onset zone (SOZ) than in other brain regions. Patient-specific HFO EDMs can facilitate the identification of the location of HFO-generating tissue, and comparison with findings from ictal recordings can provide additional useful information regarding the epileptogenic zone.

Conclusions

The distribution of interictal HFOs was reasonably consistent with the SOZ. The detection of HFO events and construction of spatial distribution maps appears to be useful for the presurgical mapping of the epileptogenic zone.     

Intraoperative subdural low-noise EEG recording of the high frequency oscillation in the somatosensory evoked potential

Objective

The detectability of high frequency oscillations (HFO, >200 Hz) in the intraoperative ECoG is restricted by their low signal-to-noise ratio (SNR). Using the somatosensory evoked HFO, we quantify how HFO detectability can benefit from a custom-made low-noise amplifier (LNA).

Outcome and complications of chronically implanted subdural electrodes for the treatment of medically resistant epilepsy

Background

Surgery for medically resistant epilepsy is safe and effective. However, when noninvasive techniques are insufficient, then consideration is given to invasive electrocorticography (EcoG).

Objective

The aim of the study was to analyze results and complications of subdural electrodes placement in the treatment of intractable epilepsy.

Methods

Ninety-one consecutive patients who underwent placement of subdural electrodes (1999-2010) were considered for this study. All patients underwent a standardized pre-operative evaluation. Invasive subdural electrode placement was considered when there were inadequate ictal recordings, there was discordance between EEG and neuroimaging or the epileptogenic zone was localized near eloquent cortex.

Results

Resective epilepsy surgery was performed in 70/91 patients (76.9%). Twenty-four out of seventy (34.3%) who underwent surgical resection were seizure-free (CL-I) at last follow-up. A statistical evaluation revealed a very strong trend for patients with positive lesional pre-operative MRI to have improved outcomes compared to normal brain MRI population (p = .028). There were 10 surgical related complications (11%), but no mortality or permanent morbidity. Statistical analysis demonstrated that placement of a subdural grid in any combination was statistically significant (p = .01) for surgical complications.

Conclusions

Invasive monitoring is a useful and necessary technique for the surgical treatment of intractable epilepsy. Careful surveillance is required during the monitoring period especially when the patient has undergone large subdural grid placement. A good working hypothesis can minimize complications and achieve better outcomes.     

Spatial Analytic Phase Difference of EEG activity during anesthetic-induced unconsciousness

Objective

A number of studies provide supporting evidence for changes in synchronization during anesthetic-induced unconsciousness. This study investigates how anesthetic administration affects the widespread patterns of phase synchrony.

Methods

The recently introduced method of Spatial Analytic Phase Difference (SAPD) was used to measure changes in synchrony in the electroencephalogram (EEG) activity of 29 patients undergoing routine surgery. Analysis was performed over 9 frequency bands: (i) δ (1.5–3.5 Hz); (ii) θ (3.5–7.5 Hz); (iii) α1 (8–10 Hz); (iv) α2 (10.5–12 Hz); (v) β1 (12.5–18 Hz); (vi) β2 (18.5–21 Hz); (vii) β3 (21.5–30 Hz); (viii) γ1 (30.5–40 Hz); and (ix) γ2 (60–80 Hz).

Results

Anesthesia was characterized by (a) large and localized synchrony increases in mid-frequency bands (8–12 Hz), (b) smaller and widespread synchrony increases in higher frequency bands (30.5–40 Hz, 60–80 Hz), and (c) both increase and decrease of synchrony in low frequency bands (1.5–7.5 Hz).

Conclusions

This study supports anesthetic-induced changes in synchrony, with the inducement of persistent and reversible widespread γ synchrony being most prominent.

Significance

Our findings have implications in the study of consciousness, support existing literature in the field and contribute towards the theoretical understanding of the mechanisms behind loss of consciousness. Future investigations could result in a synchrony-based measure for monitoring the level of hypnosis of patients during surgery.     

Towards non-invasive multi-unit spike recordings: Mapping 1 kHz EEG signals over human somatosensory cortex

Objective

Scalp-derived human somatosensory evoked potentials (SEPs) contain high-frequency oscillations (600 Hz; ‘sigma-burst’) reflecting concomitant bursts of spike responses in primary somatosensory cortex that repeat regularly at 600 Hz. Notably, recent human intracranial SEP have revealed also 1 kHz responses (‘kappa-burst’), possibly reflecting non-rhythmic spiking summed over multiple cells (MUA: multi-unit activity). However, the non-invasive detection of EEG signals at 1 kHz typical for spikes has always been limited by noise contributions from both, amplifier and body/electrode interface. Accordingly, we developed a low-noise recording set-up optimised to map non-invasively 1 kHz SEP components.

Methods

SEP were recorded upon 4 Hz left median nerve stimulation in 6 healthy human subjects. Scalp potentials were acquired inside an electrically and magnetically shielded room using low-noise custom-made amplifiers. Furthermore, in order to reduce thermal Johnson noise contributions from the sensor/skin interface, electrode impedances were adjusted to ?1 kΩ. Responses averaged after repeated presentation of the stimulus (n = 4000 trials) were evaluated by spatio-temporal pattern analyses in complementary spectral bands.

Results

Three distinct spectral components were identified: N20 (<100 Hz), sigma-burst (450–750 Hz), and kappa-burst (850–1200 Hz). The two high-frequency bursts (sigma, kappa) exhibited distinct and partially independent spatiotemporal evolutions, indicating subcortical as well as several cortical generators.

Conclusions

Using a dedicated low-noise set-up, human SEP ‘kappa-bursts’ at 1 kHz can be non-invasively detected and their scalp distribution be mapped. Their topographies indicate a set of subcortical/cortical generators, at least partially distinct from the topography of the 600 Hz sigma-bursts described previously.

Significance

The non-invasive detection and surface mapping of 1 kHz EEG signals presented here provides an essential step towards non-invasive monitoring of multi-unit spike activity.     

Is interictal EEG activity a biomarker for mood disorders in temporal lobe epilepsy?

Objective

Psychiatric comorbidities are frequent in temporal lobe epilepsy (TLE), and symptoms of these comorbidities may be related to epilepsy activity. Here we evaluated interictal EEG activity in TLE patients with or without psychiatric comorbidities.

Methods

A cohort study of 78 patients with TLE, with evaluation of wake/sleep interictal scalp EEG. All subjects were submitted to a psychiatric structured clinical interview (SCID) for the diagnosis of lifetime psychiatric comorbidities. Three major diagnostic categories were studied: mood disorders, anxiety disorders, and psychosis. We then evaluated differences in interictal EEG activity between patients with and without these psychiatric comorbidities.

Results

Infrequent EEG interictal spikes, defined as less than one event per minute, were significantly associated with mood disorders in TLE (p = 0.02).

Conclusions

Low intensity seizure disorder has been associated with a decrease in interictal EEG discharges and with an increase in psychiatric symptoms in TLE, a phenomenon known as forced normalization. In our study, we observed a low interictal spike frequency on EEG in TLE patients with mood disorders.

Significance

A low spike index might be a neurophysiological marker for depression in temporal lobe epilepsy.     

Cortical sources of resting-state EEG rhythms are abnormal in naïve HIV subjects

Objective

The aim of the study was to test the hypothesis that cortical sources of resting-state electroencephalographic (EEG) rhythms show peculiar frequency/spatial features in naïve human subjects with human immunodeficiency virus (HIV) compared to healthy control subjects.

Methods

Resting-state eyes-closed EEG data were recorded in 18 naïve HIV subjects (15 males; mean age 39 years ± 2.0 standard error of mean, SEM) and in 18 age-matched cognitively normal subjects (15 males; 38.7 years ± 2.2 SEM). EEG rhythms of interest were delta (2–4 Hz), theta (4–8 Hz), alpha1 (8–10 Hz), alpha2 (10–12 Hz), beta1 (13–20 Hz) and beta2 (20–30 Hz). Cortical EEG sources were estimated by normalised, low-resolution electromagnetic tomography (LORETA).

Results

Mini Mental State Evaluation (MMSE) score was lower in HIV (26.5 ± 0.7 SEM) than in healthy (29.2 ± 0.5 SEM) subjects (p < 0.05). Central and parietal delta sources showed higher amplitude in the HIV than in control subjects. Furthermore, topographically widespread, cortical sources of resting-state alpha rhythms were lower in amplitude in HIV subjects than in control subjects.

Conclusions

The present results suggest that topography and frequency of the cortical sources of resting-state EEG rhythms can distinguish groups of HIV and control subjects.

Significance

These results encourage future studies in an enlarged cohort of HIV subjects to test the hypothesis that the present methodological approach provides clinically useful information for an early detection of the effect of HIV infection on brain and cognitive functions.     

Slow spindles’ cortical generators overlap with the epileptogenic zone in temporal epileptic patients: An electrical source imaging study

Objective

To determine whether temporal epileptic patients and normal volunteers display similar sleep spindles’ cortical generators as determined by electrical source imaging (ESI), and whether such generators overlap in epilepsy patients with the epileptogenic zone identified by ESI.

Methods

Twelve healthy subjects and twelve temporal lobe pharmaco-resistant epileptic patients underwent a 256-channel EEG recording during a daytime nap. Sleep spindles were analyzed off line, distinguishing slow (10–12 Hz) and fast (12–14 Hz) ones, and the final averaged signal was projected onto a MNI (Montreal Neurological Institute) space to localize cortical generators. The same procedure was performed for averaged epileptic spikes, obtaining their cortical source. Intra- and inter-group statistical analyses were conducted.

Results

Multiple, concomitant generators were detected in both populations for slow and fast spindles. Slow spindles in epileptics displayed higher source amplitude in comparison to healthy volunteers (Z = 0.001), as well as a preferential localization over the affected temporal cortices (p = 0.039). Interestingly, at least one of slow spindles’ generators overlapped with the epileptogenic zone.

Conclusion

Slow spindles, but not fast ones, in temporal epilepsy are mainly generated by the affected temporal lobe.

Significance

These results point to the strict relation between sleep and epilepsy and to the possible cognitive implications of spikes arising from memory-encoding brain structures.     

Resting state eyes-closed cortical rhythms in patients with locked-in-syndrome: An eeg study

Objective

Locked-in syndrome (LIS) is a state of complete paralysis, except for ocular movements, which results from ventral brainstem lesions. Patients typically are fully conscious. Here we tested the hypothesis that electroencephalographic (EEG) rhythms are abnormal in LIS patients, possibly due to an impaired neural synchronization between brainstem and cerebral cortex.

Methods

Resting state eyes-closed EEG data were recorded in 13 LIS subjects and 15 cognitively normal control subjects. With reference to the individual alpha frequency (IAF), the bands of interest were delta (IAF-8 to IAF-6 Hz), theta (IAF-6 to IAF-4 Hz), alpha 1 (IAF-4 to IAF-2 Hz), alpha 2 (IAF-2 to IAF Hz), and alpha 3 (IAF to IAF + 2 Hz). Furthermore, beta 1 (13–20 Hz) and beta 2 (20–30 Hz) bands were also considered. Cortical EEG sources were estimated by low-resolution electromagnetic tomography (LORETA).

Results

The power of alpha 2 and alpha 3 sources in all regions was lower in patients with LIS compared to controls. The power of delta sources in central, parietal, occipital and temporal regions was higher in patients with LIS compared to controls.

Conclusions

These results suggest that cortical sources of resting state eyes-closed alpha and delta rhythms are abnormal in LIS patients.

Significance

LIS is accompanied by a functional impairment of cortical neuronal synchronization mechanisms in the resting state condition.     

Effects of repetition rate of bone-conducted vibration on ocular and cervical vestibular-evoked myogenic potentials

Objective

This study applied bone-conducted vibration (BCV) stimuli at various repetition rates to investigate the effects of repetition rate on both ocular and cervical vestibular-evoked myogenic potentials (oVEMPs and cVEMPs).

Methods

Twenty-five healthy subjects underwent oVEMP tests in BCV mode at repetition rates of 1, 5, 10, 20, 30 and 40 Hz. The optimal repetition rates (5, 10 and 20 Hz) for oVEMPs were also adopted to elicit cVEMPs, and 20 Hz stimuli were further evaluated in pathological ears.

Results

At repetition rates of 1, 5, 10, 20, 30 and 40 Hz, the prevalence of clear oVEMPs were 100% in groups of 5, 10 and 20 Hz, with no significant differences in the mean nI latency, but the mean nI–pI amplitude of the 20 Hz group showed significantly larger. For the BCV–cVEMPs, 5, 10 and 20 Hz stimuli yielded similar information. Clinically, the BCV mode at 20 Hz stimuli was also appropriate for evaluating VEMPs in ears of vestibular schwannoma.

Conclusions

The BCV mode at a repetition rate of 20 Hz is recommended for the mass detection of VEMPs.

Significance

Eliciting VEMPs in BCV mode using 20 Hz stimuli takes a short time and may trigger a high prevalence with large amplitude.     

Electrophysiological intermediate biomarkers for oxidative stress in schizophrenia

Objective

Diverse electrophysiological abnormalities have been associated with schizophrenia, but the underlying causes remain elusive. We tested whether the altered oxidative stress in schizophrenia contributes to the electrophysiological abnormalities.

Methods

We used an auditory oddball task to measure mismatch negativity (MMN) and gamma band response on 29 schizophrenia patients and 25 normal controls. Oxidative stress was assessed by monomeric glutathione (GSH, reduced form) and glutathione disulfide (GSSG, oxidized form).

Results

Patients had reduced MMN (p = 0.015) and reduced power of gamma band responses at 21–40 Hz and 41–85 Hz (all p < 0.001). GSH was significantly lower (p < 0.001) while %GSSG was higher (p = 0.023) in patients compared with controls. MMN was correlated with GSH in controls; while 21–40 Hz responses were correlated with GSH in patients. Lower GSH and higher GSSG levels were associated with low community functioning (p = 0.018). Multivariate mediation modeling showed that gamma band at 21–40 Hz was a significant mediator for GSH effect on community functions.

Conclusions

High beta/low gamma range (21–40 Hz) responses may be an intermediate biomarker indexing oxidative stress and its effect on clinical functions.

Significance

Electrophysiological abnormalities and associated clinical functional changes may in part be associated with heightened oxidative stress in schizophrenia.     

Intracerebrally recorded high frequency oscillations: Simple visual assessment versus automated detection

Objective

We compared the possible contribution (in the detection of seizure onset zone – SOZ) of simple visual assessment of intracerebrally recorded high-frequency oscillations (HFO) with standard automated detection.

Methods

We analyzed stereo-EEG (SEEG) recordings from 20 patients with medically intractable partial seizures (10 temporal/10 extratemporal). Independently using simple visual assessment and automated detection of HFO, we identified the depth electrode contacts with maximum occurrences of ripples (R) and fast ripples (FR). The SOZ was determined by independent visual identification in standard SEEG recordings, and the congruence of results from visual versus automated HFO detection was compared.

Results

Automated detection of HFO correctly identified the SOZ in 14 (R)/10 (FR) out of 20 subjects; a simple visual assessment of SEEG recordings in the appropriate frequency ranges correctly identified the SOZ in 13 (R)/9 (FR) subjects.

Conclusions

Simple visual assessment of SEEG traces and standard automated detection of HFO seem to contribute comparably to the identification of the SOZ in patients with focal epilepsies. When using macroelectrodes in neocortical extratemporal epilepsies, the SOZ might be better determined by the ripple range.

Significance

Standard automated detection of HFO enables the evaluation of HFO characteristics in whole data. This detection allows general purpose and objective evaluation, without any bias from the neurophysiologist’s experiences and practice.     

Cortical sources of resting state EEG rhythms are abnormal in dyslexic children

Objective

Previous studies have been inconclusive whether dominant resting state alpha rhythms differ in amplitude in dyslexic subjects when compared to control subjects, being these rhythms considered as a reflection of effective cortical neural synchronization and cognition. Here we used a validated EEG source estimation to test the hypothesis that resting state alpha rhythms are abnormal in dyslexic subjects and are related to reading deficits.

Methods

Eyes-closed resting state electroencephalographic (EEG) data were recorded in 26 dyslexics (12 males, mean age of 11 years ± 0.5 standard error of mean, SEM) and 11 age-matched normal control subjects (8 males, mean age of 11 years ± 0.7 SEM). EEG rhythms of interest, based on individual alpha frequency peak, were the following: about 2–4 Hz (delta), 4–6 Hz (theta), 6–8 Hz (alpha 1), 8–10 Hz (alpha 2), and 10–12 Hz (alpha 3). For the higher frequencies, we selected beta 1 (13–20 Hz), beta 2 (20–30 Hz), and gamma (30–40 Hz). Cortical EEG sources were estimated by low resolution electromagnetic tomography (LORETA). LORETA solutions were normalized across all voxels and frequencies.

Results

Compared to the control children, the dyslexics showed lower amplitude of parietal, occipital, and temporal alpha 2 and alpha 3 sources. In the dyslexics, some of these sources were correlated to reading time of pseudo-words (parietal alpha 2, r = −0.56, p = 0.02; parietal alpha 3, r = −0.58, p = 0.02; temporal alpha 3, r = −0.57, p = 0.02); the higher the alpha power, the shorter the reading time.

Conclusions

Dyslexic children are characterized by limited abnormalities of resting state EEG rhythms as to topography (posterior regions) and frequency (alpha), which were related to phonological encoding (pseudo-words reading).

Significance

Dyslexia may be associated to some functional impairment of cortical neuronal synchronization mechanisms involved in the resting state condition.     

Intracranially recorded interictal spikes: Relation to seizure onset area and effect of medication and time of day

Objective

The relationship between seizures and interictal spikes remains undetermined. We analyzed intracranial EEG (icEEG) recordings to examine the relationship between the seizure onset area and interictal spikes.

Methods

80 unselected patients were placed into 5 temporal, 4 extratemporal, and one unlocalized groups based on the location of the seizure onset area. We studied 4-h icEEG epochs, removed from seizures, from day-time and night-time during both on- and off-medication periods. Spikes were detected automatically from electrode contacts sampling the hemisphere ipsilateral to the seizure onset area.

Results

There was a widespread occurrence of spikes over the hemisphere ipsilateral to the seizure onset area. The spatial distributions of spike rates for the different patient groups were different (p < 0.0001, chi-square test). The area with the highest spike rate coincided with the seizure onset area only in half of the patients.

Conclusion

The spatial distribution of spike rates is strongly associated with the location of the seizure onset area, suggesting the presence of a distributed spike generation network, which is related to the seizure onset area.

Significance

The spatial distribution of spike rates, but not the area with the highest spike rate, may hold value for the localization of the seizure onset area.     

Characteristics of temporal lobe epilepsy with no ictal impairment of consciousness

Introduction

The predominant manifestations of temporal lobe epilepsy (TLE) are partial seizures with impairment of consciousness (type I.B of ILAE classification), although consciousness impairment is not necessary in all seizures of patients with TLE. Nevertheless, there have been very few reports of TLE patients with exclusive seizures with no impairment of consciousness (i.e. isolated auras). The objective of this study was to determine any differential characteristics of this subgroup of TLE patients.

Material and methods

Retrospective case-control study in 163 consecutive TLE patients from our hospital database. The patients were divided between those with and without ictal impairment of consciousness, based on directed semi-structured questionnaire to the patient and relatives and on video–EEG records. Ten independent variables (8 clinical and 2 paraclinical) were compared between the groups.

Results

14 patients (8.5%) formed the “TLE without ictal impairment of consciousness” group. This group was less refractory to medical treatment [Odds Ratio: 0.14 (0.03–0.64); p < 0.01] and had frequent ictal motor behaviour [Odds ratio: 5.33 (1.65–17.14); p = 0.008] and less frequent presence of automatisms [p < 0.001]. Non-significant tendencies were observed for a higher frequency of lesional substrate and fewer generalization episodes.

Discussion

TLE without ictal impairment of consciousness appears to be more frequent than previously thought. This subgroup of TLE patients shows differential characteristics that may possibly result from a differential propagation of the original epileptic activity towards frontal areas rather than towards neocortical and diencephalic structures, which may be related to the more frequent presence of structural lesions.     

The EEG response to photic stimulation is not increased in alcohol-related seizures

Objective

To investigate the occipital EEG response to 18 and 24 Hz photic stimulation (the H-response) in alcohol-related seizures (ARS).

Method

Twenty-two ARS patients, 15 of whom had a withdrawal seizure (WS) were compared with patients with recent seizures of other causes: 21 patients with epilepsy, and 30 Alcohol Use Disorders Identification Test (AUDIT) negative patients with other seizures. EEG from 37 out-patients with epilepsy and 79 sciatica patents served as patient-controls. The spectral amplitude around 18 and 24 Hz and a new photic H-ratio (24/18 Hz relative amplitude) was calculated.

Results

The H-ratio was significantly reduced in the ARS group compared to the sciatica group. H-ratio reduction correlated with the AUDIT score in ARS patients (p = 0.02). No differences between WS and non-WS patients were found for H-response variables.

Conclusion

A dose–response relationship between AUDIT and the photic response H-ratio was observed in ARS patients. The EEG-driving response to 24 Hz flashes was not increased in ARS.

Significance

The relative decrease in 24 Hz photic response in ARS reflected drinking severity. The H-ratio is a candidate biomarker for ARS on the group level, although the moderate effect size precludes its use in individual patients.     

Enhancing plasticity through repeated rTMS sessions: The benefits of a night of sleep

Objective

Previous work has demonstrated that corticospinal facilitation from 20 Hz repetitive transcranial magnetic stimulation (rTMS) was greater during a second rTMS session 24 h after the first. We sought to determine whether such metaplasticity is dependent on a particular phase of the normal sleep–wake/circadian cycle.

Methods

Twenty healthy participants received two sessions of 20 Hz rTMS over the hand motor cortex (M1) spaced 12 h apart, either over-day or overnight.

Results

Baseline corticospinal excitability did not differ by group or session. The time-of-day of Session 1 did not influence the relative increase in excitability following rTMS. However, the increase in excitability from the second rTMS session was 2-fold greater in the overnight group.

Conclusions

When a night with sleep follows rTMS to M1, the capacity to induce subsequent plasticity in M1 is enhanced, suggesting sleep–wake and/or circadian-dependent modulation of processes of metaplasticity.

Significance

TMS treatment of neuropsychiatric disorders entails repeated sessions of rTMS. Our findings suggest that the timing of sessions relative to the sleep–wake/circadian cycle may be a critical factor in the cumulative effect of treatment. Future studies using this paradigm may provide mechanistic insights into human metaplasticity, leading to refined strategies to enhance non-invasive stimulation therapies.     

Outcomes in octogenarians with subdural hematomas

Objective

In the majority of literature concerning age in TBI, specifically in subdural hematomas (SDH), the mean age of patients considered elderly is 55–65. Limited data in SDH patients > 75 years suggest an increased mortality rate. The impact of medical decision making on these data is not well-documented.

Patients/Methods

We use the Nationwide Inpatient Sample (NIS) database to compare outcomes between SDH patients 60–79 and ≥80. As administrative databases have some shortcomings, i.e. in-hospital data only, acute and chronic SDHs listed together, we examined institutional data to evaluate the impact of these factors on medical decision making which may falsely elevate mortality rates.

Results

In-hospital mortality was increased in NIS patients > 80 treated both surgically and non-surgically (P < 0.05). Our institutional data confirmed higher in-hospital mortality rates in patients > 80 with SDHs as a group. However, the SDH patients > 80 who underwent surgery at our institution had much lower mortality rates. We found that patients ≥ 80 made up 87% of all patients with “surgical lesions” that were not operated on. Type of subdural, admission GCS, and baseline cognitive status appeared to have a significant impact on surgical decision making.

Conclusion

This study examines mortality rates in patients > 80 with SDHs who are managed surgically and non-surgically using a large administrative database and institutional data. It provides preliminary insight into medical decision making which make affect mortality rates of the very elderly.     

Modulation of visual evoked potentials by high-frequency repetitive transcranial magnetic stimulation in migraineurs

Objective

High-frequency repetitive transcranial magnetic stimulation (rTMS) modulates cortical excitability. We investigated its effect on visual evoked potentials (VEPs) in migraine.

Methods

Thirty-two headache-free controls (CO), 25 interictal (MINT) and 7 preictal migraineurs (MPRE) remained after exclusions. VEPs to 8′ and 65′ checks were averaged in six blocks of 100 single responses. VEPs were recorded before, directly after and 25 min after 10 Hz rTMS. The study was blinded for diagnosis during recording and for diagnosis and block number during analysis. First block amplitudes and habituation (linear amplitude change over blocks) were analysed with repeated measures ANOVA.

Results

With 65′ checks, N70-P100 habituation was reduced in MINT compared to CO after rTMS (p = 0.013). With 8′ checks, habituation was reduced in MPRE compared to MINT and CO after rTMS (p < 0.016). No effects of rTMS on first block amplitudes were found.

Conclusion

RTMS reduced habituation only in migraineurs, indicating increased responsivity to rTMS. The magnocellular visual subsystem may be affected interictally, while the parvocellular system may only be affected preictally.

Significance

Migraineurs may have increased responsiveness to rTMS because of a cortical dysfunction that changes before a migraine attack.