Neural networks for processing language often are reorganized in patients with epilepsy. However, the extent and location of within and between hemisphere re-organization are not established. We studied 45 patients, all with a left hemisphere seizure focus (mean age 22.8, seizure onset 13.3), and 19 normal controls (mean age 24.8) with an fMRI word definition language paradigm to assess the location of language processing regions. Individual patient SPM maps were compared to the normal group in a voxel-wise comparison; a voxel was considered to be significant if its z-value exceeded mid R:2mid R:. Subsequently, we used principal component analysis with hierarchical clustering of variance patterns from individual difference maps to identify four patient sub-groups. One did not differ from normal controls; one had increased left temporal activation on the margin of regions activated in controls; two others had recruitment in right inferior frontal gyrus, middle frontal gyrus and temporal cortex. Right hemisphere activation in these two groups occurred in homologues of left hemisphere regions that sustained task activation. Our study used novel data driven methods to find evidence for constraints on inter-hemispheric reorganization of language in recruitment of right homologues, and, in a subpopulation of patients, evidence for intra-hemispheric reorganization of language limited to the margins of typical left temporal regional activation. These methods may be applied to investigate both normal and pathological variance in other developmental disorders and cognitive domains.
Objective: Succinic semialdehyde dehydrogenase (SSADH) deficiency is an autosomal recessive disorder of GABA metabolism characterized by elevated levels of GABA and gammahydroxybutyric acid. Clinical findings include intellectual impairment, hypotonia, hyporeflexia, hallucinations, autistic behaviors, and seizures. Autoradiographic labeling and slice electrophysiology studies in the murine model demonstrate use-dependent downregulation of GABA(A) receptors. We studied GABA(A) receptor activity in human SSADH deficiency utiliz- Succinic semialdehyde dehydrogenase (SSADH) deficiency, also called 4-hydroxybutyric aciduria (McKusick 279180) and aldehyde dehydrogenase 5a1 (Aldh5a1), is an autosomal recessive disorder. About 350 patients are known, with about 85% under 18, making this the most prevalent pediatric neurotransmitter disorder. 1 In the absence of SSADH, transamination of GABA to succinic semialdehyde is followed by its conversion to 4-hydroxybutryic acid (gamma-hydroxybutyric acid, or GHB), leading to CNS GABA and ␥-hydroxy butyrate (GHB) accumulation.2 Major clinical manifestations include developmental delay, hypotonia, ataxia, and seizures. Hyperkinetic behavior, aggression, self-injurious behaviors, and hallucinations have also been described; EEG abnormalities include generalized and focal epileptiform discharges, photosensitivity, and background slowing.
Objective: To investigate interhemispheric and intrahemispheric reorganization in patients with localization-related epilepsy. Method:We studied 50 patients with a left hemispheric focus and 20 normal right-handed controls with a 3T echoplanar imaging blood oxygen level dependent functional MRI auditory-based word definition decision task. Data were analyzed using SPM 2. Using region of interest for Broca and Wernicke areas and an asymmetry index (AI), patients were categorized as left language (LL; AI Ն0.20) or atypical language (AL; AI Ͻ0.20) for region. The point maxima activation for normal controls (p Ͻ0.05 corrected FDR) was identified in Broca and midtemporal regions and then used as a point of reference for individual point maxima identified at p Ͻ 0.001, uncorrected. Results:Patient groups showed increased frequency of having activation in right homologues.Activation in AL groups occurred in homologous right regions; distances for point maxima activation in homologous regions were the same as point maxima distances in normal control activation in left regions. Distances for LL patient in left regions showed a trend for differences for midtemporal gyrus (6 mm posterior, 3 mm superior) but variability around mean difference distance was significant. There was no effect of age at epilepsy onset, duration, or pathology on activation maxima. The ability to process language typically resides in the left hemisphere. Conclusions:1,2 Atypical language dominance occurs in 4%-6% of the normal right-handed population and 22%-24% of normal left-handed individuals.3,4 MRI is effective in determining language lateralization as well as identifying the location of language processing areas. 5,6 Functional MRI (fMRI) may also be used to describe the effects of epilepsy on language networks as well as assisting in presurgical planning. [7][8][9] Patients with epilepsy, regardless of handedness, have a high likelihood of atypical language.3,10,11 Early cortical injury or epileptic activity may ultimately lead to language reorganization. 11,12 The younger the brain insult, if focal, the more likely the reorganization of language functions occurs with preservation of function. 2,13 Patients with a seizure focus in the left temporal lobe are more likely to have language activation in the right hemisphere.
Summary Purpose Arterial spin labeling (ASL) is a developing magnetic resonance imaging (MRI) method for noninvasive measurement of cerebral blood flow (CBF). The purpose of this study was to evaluate the usefulness of ASL for detecting interictal temporal hypoperfusion in temporal lobe epilepsy (TLE). ASL-derived CBF measurements were compared with those derived from H215O positron emission tomography (PET). Methods 11 normal controls and 10 patients with medically intractable TLE were studied. Pulsed ASL (PASL) with quantitative imaging of perfusion using a single subtraction, second version (QUIPSS II) was performed in all subjects and H215O PET was performed in patients. Regional CBF values in the mesial and lateral temporal lobes were measured utilizing quantitative analysis of perfusion images. A perfusion asymmetry index (AI) was calculated for each region. Results In patients, mean CBF in the mesial temporal lobe was not significantly different between PASL and H215O PET, and ipsilateral mesial temporal CBF was lower than contralateral CBF with both techniques. PASL detected significant mesial temporal perfusion asymmetry agreeing with EEG laterality in four patients. H215O PET found ipsilateral interictal hypoperfusion in three. Both scans found unilateral hypoperfusion in one patient with bilateral EEG discharges. Conclusions Pulsed ASL may be a promising approach to detecting interictal hypoperfusion in TLE. This method has potential as a clinical alternative to H215O PET due to noninvasiveness and easy accessibility.
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