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Khalid Hamandi

Publications and source records attributed to Khalid Hamandi.

11 recordsLinked to original sources
PubMed2007

Temporal lobe interictal epileptic discharges affect cerebral activity in "default mode" brain regions.

A cerebral network comprising precuneus, medial frontal, and temporoparietal cortices is less active both during goal-directed behavior and states of reduced consciousness than during conscious rest. We tested the hypothesis that the interictal epileptic discharges affect activity in these brain regions in patients with temporal lobe epilepsy who have complex partial seizures. At the group level, using electroencephalography-correlated functional magnetic resonance imaging in 19 consecutive patients with focal epilepsy, we found common decreases of resting state activity in 9 patients with temporal lobe epilepsy (TLE) but not in 10 patients with extra-TLE. We infer that the functional consequences of TLE interictal epileptic discharges are different from those in extra-TLE and affect ongoing brain function. Activity increases were detected in the ipsilateral hippocampus in patients with TLE, and in subthalamic, bilateral superior temporal and medial frontal brain regions in patients with extra-TLE, possibly indicating effects of different interictal epileptic discharge propagation.

Auditory Cortex↗
PubMed2006

Hemodynamic correlates of epileptiform discharges: an EEG-fMRI study of 63 patients with focal epilepsy.

Using continuous EEG-correlated fMRI, we investigated the Blood Oxygen Level Dependent (BOLD) signal correlates of interictal epileptic discharges (IEDs) in 63 consecutively recruited patients with focal epilepsy. Semi-automated spike detection and advanced modeling strategies are introduced to account for different EEG event types, and to minimize false activations from uncontrolled motion. We show that: (1) significant hemodynamic correlates were detectable in over 68% of patients in whom discharges were captured and were highly, but not entirely, concordant with site(s) of presumed seizure generation where known; (2) deactivations were less concordant and may non-specifically reflect the consequential or downstream effects of IEDs on brain activity; (3) a striking pattern of retrosplenial deactivation was observed in 7 cases mainly with focal discharges; (4) the basic hemodynamic response to IEDs is physiological; (5) incorporating information about different types of IEDs, their durations and saturation effects resulted in more powerful models for the detection of fMRI correlates; (6) focal activations were more likely when there was good electroclinical localization, frequent stereotyped spikes, less head motion and less background EEG abnormality, but were also seen in patients in whom the electroclinical focus localization was uncertain. These findings provide important new information on the optimal use and interpretation of EEG-fMRI in focal epilepsy and suggest a possible role for EEG-fMRI in providing new targets for invasive EEG monitoring.

Adult↗
PubMed2006

EEG-fMRI of idiopathic and secondarily generalized epilepsies.

We used simultaneous EEG and functional MRI (EEG-fMRI) to study generalized spike wave activity (GSW) in idiopathic and secondary generalized epilepsy (SGE). Recent studies have demonstrated thalamic and cortical fMRI signal changes in association with GSW in idiopathic generalized epilepsy (IGE). We report on a large cohort of patients that included both IGE and SGE, and give a functional interpretation of our findings. Forty-six patients with GSW were studied with EEG-fMRI; 30 with IGE and 16 with SGE. GSW-related BOLD signal changes were seen in 25 of 36 individual patients who had GSW during EEG-fMRI. This was seen in thalamus (60%) and symmetrically in frontal cortex (92%), parietal cortex (76%), and posterior cingulate cortex/precuneus (80%). Thalamic BOLD changes were predominantly positive and cortical changes predominantly negative. Group analysis showed a negative BOLD response in the cortex in the IGE group and to a lesser extent a positive response in thalamus. Thalamic activation was consistent with its known role in GSW, and its detection in individual cases with EEG-fMRI may in part be related to the number and duration of GSW epochs recorded. The spatial distribution of the cortical fMRI response to GSW in both IGE and SGE involved areas of association cortex that are most active during conscious rest. Reduction of activity in these regions during GSW is consistent with the clinical manifestation of absence seizures.

Adolescent↗
PubMed2006

EEG-fMRI mapping of asymmetrical delta activity in a patient with refractory epilepsy is concordant with the epileptogenic region determined by intracranial EEG.

We studied a patient with refractory focal epilepsy using continuous EEG-correlated fMRI. Seizures were characterized by head turning to the left and clonic jerking of the left arm, suggesting a right frontal epileptogenic region. Interictal EEG showed occasional runs of independent nonlateralized slow activity in the delta band with right frontocentral dominance and had no lateralizing value. Ictal scalp EEG had no lateralizing value. Ictal scalp EEG suggested right-sided central slow activity preceding some seizures. Structural 3-T MRI showed no abnormality. There was no clear epileptiform abnormality during simultaneous EEG-fMRI. We therefore modeled asymmetrical EEG delta activity at 1-3 Hz near frontocentral electrode positions. Significant blood oxygen level-dependent (BOLD) signal changes in the right superior frontal gyrus correlated with right frontal oscillations at 1-3 Hz but not at 4-7 Hz and with neither of the two frequency bands when derived from contralateral or posterior electrode positions, which served as controls. Motor fMRI activations with a finger-tapping paradigm were asymmetrical: they were more anterior for the left hand compared with the right and were near the aforementioned EEG-correlated signal changes. A right frontocentral perirolandic seizure onset was identified with a subdural grid recording, and electric stimulation of the adjacent contact produced motor responses in the left arm and after discharges. The fMRI localization of the left hand motor and the detected BOLD activation associated with modeled slow activity suggest a role for localization of the epileptogenic region with EEG-fMRI even in the absence of clear interictal discharges.

Brain Mapping↗
PubMed2006

Analysis of EEG-fMRI data in focal epilepsy based on automated spike classification and Signal Space Projection.

Simultaneous acquisition of EEG and fMRI data enables the investigation of the hemodynamic correlates of interictal epileptiform discharges (IEDs) during the resting state in patients with epilepsy. This paper addresses two issues: (1) the semi-automation of IED classification in statistical modelling for fMRI analysis and (2) the improvement of IED detection to increase experimental fMRI efficiency. For patients with multiple IED generators, sensitivity to IED-correlated BOLD signal changes can be improved when the fMRI analysis model distinguishes between IEDs of differing morphology and field. In an attempt to reduce the subjectivity of visual IED classification, we implemented a semi-automated system, based on the spatio-temporal clustering of EEG events. We illustrate the technique's usefulness using EEG-fMRI data from a subject with focal epilepsy in whom 202 IEDs were visually identified and then clustered semi-automatically into four clusters. Each cluster of IEDs was modelled separately for the purpose of fMRI analysis. This revealed IED-correlated BOLD activations in distinct regions corresponding to three different IED categories. In a second step, Signal Space Projection (SSP) was used to project the scalp EEG onto the dipoles corresponding to each IED cluster. This resulted in 123 previously unrecognised IEDs, the inclusion of which, in the General Linear Model (GLM), increased the experimental efficiency as reflected by significant BOLD activations. We have also shown that the detection of extra IEDs is robust in the face of fluctuations in the set of visually detected IEDs. We conclude that automated IED classification can result in more objective fMRI models of IEDs and significantly increased sensitivity.

Cerebral Cortex↗
PubMed2006

Pregabalin: a new antiepileptic drug for refractory epilepsy.

Pregabalin is a recently licensed and marketed antiepileptic drug for use as adjunctive treatment of partial epilepsy. It acts at presynaptic calcium channels, modulating neurotransmitter release in the CNS, properties it shares with gabapentin. Its clinical development over the past decade has included its use in the treatment of neuropathic pain, and generalized anxiety disorder, in addition to epilepsy. Three multi-centre randomised, double-blind, placebo-controlled trials enrolling patients with refractory partial epilepsy have demonstrated an antiepileptic effect of pregabalin against placebo, as adjunctive therapy, with 31-51% of patients showing a 50% reduction in seizure frequency. Adverse effects were dose related, the commonest being somnolence, dizziness, and ataxia. Weight gain was seen in 14% of patients on the highest dose of 600 mg/day. Around 9000 people have been exposed to pregabalin in its development for all indications. No idiosyncratic reactions have been described to date. Pregabalin may be a useful addition in the treatment of refractory partial epilepsy. As with all new AEDs long-term follow up and post marketing surveillance is required.

Adolescent↗
PubMed2006

Linking generalized spike-and-wave discharges and resting state brain activity by using EEG/fMRI in a patient with absence seizures.

PURPOSE: To illustrate a functional interpretation of blood oxygen level-dependent (BOLD) signal changes associated with generalized spike-and-wave discharges in patients with absence seizures and to demonstrate the reproducibility of these findings in one case. METHODS: In a 47 year-old patient with frequent absence seizures, BOLD signal changes during generalized spike-and-wave discharges (GSWD) were mapped by using simultaneous and continuous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) at 1.5 T and 6 months later at 3 T. GSWDs were modeled as individual events and as blocks. RESULTS: The patient studied exhibited frequent generalized spike-wave activity with temporal properties ideal for study with EEG/fMRI. Highly reproducible GSWD-associated fMRI signal decreases (deactivations) were seen in bilateral frontal and temporoparietal cortices and the precuneus, in addition to activations in occipital cortex and, at 3 T, the posterior thalamus. CONCLUSIONS: The GSWD-associated changes seen here involve cortical regions that have been shown to be more active at conscious rest compared with sleep and with various types of extroverted perception and action. These regions have been proposed to constitute the core of a functional "default mode" system. We propose that the findings of deactivation of this distributed brain system during GSWDs mirrors the clinical manifestation of GSWDs (i.e., absence seizures). Furthermore, we suggest that these deactivations may reflect the functional consequences of GSWDs on physiologic brain activity at rest rather than direct hemodynamic correlates of epileptic discharges.

Brain↗
PubMed2004

The MR detection of neuronal depolarization during 3-Hz spike-and-wave complexes in generalized epilepsy.

Previously, an analysis of activations observed in a patient with idiopathic generalized epilepsy using electroencephalogram-correlated functional magnetic resonance imaging (MRI) during runs of 3-Hz generalized spike-wave discharge (GSWD) was presented by Salek-Haddadi. Time-locked, bilateral, thalamic blood oxygenation level-dependent increases were reported to be accompanied by widespread, symmetric, cortical deactivation with a frontal maximum. In light of recent investigations into MRI detection of the magnetic field perturbations caused by neuronal current loops during depolarization, we revisited the analysis of the data of Salek-Haddadi as a preliminary search for a neuroelectric signal. We modeled the MRI response as the sum of a fast signal and a slower signal and demonstrated significant MRI activity at a time scale of the order of 30 ms associated with GSWDs. Further work is necessary before firm conclusions may be drawn about the nature of this signal.

Cerebral Cortex↗
PubMedDate not supplied

EEG/functional MRI in epilepsy: The Queen Square Experience.

The recording of EEG during functional MRI scanning (EEG/fMRI) has opened up new dimensions in brain research. The simultaneous recording of EEG activity and its temparospatial haemodynamic correlates is a powerful tool in the non-invasive mapping of normal and pathological brain function. The technological constraints imposed by having a conductor (the EEG) within the magnetic environment of the MRI scanner have been sufficiently overcome for high quality EEG recording during MRI. The initial applications of EEG/fMRI were in the study of epileptiform discharges in epilepsy. This has been rapidly followed by studies of normal EEG rhythms and evoked response in healthy subjects. The ability to map brain areas involved in the generation of epileptiform discharges recorded on the surface EEG has been shown using EEG/fMRI in patients with epilepsy. This has potential clinical applications in providing additional localizing information in the pre-surgical workup of epilepsy patients and in gaining a greater understanding of the neurobiology of interictal epileptiform discharges and epileptic seizures. In this review we address the issues in recording EEG during fMRI and review the application of EEG/fMRI in the study of patients with epilepsy at our centre.

Cerebrovascular Circulation↗