Hippocampal Activation during Verbal Encoding Separates Patients with Left Mesial Temporal Sclerosis from Controls.
Abstract number :
1.244
Submission category :
Year :
2001
Submission ID :
271
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
S.C. Johnson, Ph.D., Neuropsychology, Barrow Neurological Institute, Phoenix, AZ; L.C. Baxter, Ph.D., Neuropsychology, Barrow Neurological Institute, Phoenix, AZ; D.E. Blum, MD, Neurology, Barrow Neurological Institute, Phoenix, AZ
RATIONALE: Memory functioning is frequently impaired in temporal lobe epilepsy, presumably due to hippocampal sclerosis. Although neuropsychological testing and the intracarotid amobarbital test are both commonly used to evaluate memory functioning in surgical candidates, the spatial resolution of these procedures is limited. In this study, functional MRI (fMRI) was used as a probe of memory encoding of novel words in patients with left hippocampal sclerosis and healthy controls.
METHODS: Five epilepsy patients (mean age 38; 3m/2f) with left mesial temporal sclerosis (MTS) and 6 healthy volunteers (mean age 29, 3m/3f) participated. Fifteen minutes prior to the functional scanning, participants were shown four words repeatedly for eight minutes. Words were presented visually, one at a time, every three seconds. During the fMRI scan, participants saw novel words intermixed pseudorandomly with the overlearned (old) words and null events. Scanning parameters were as follows: TE=40ms, TR=3000ms, FOV= 240mm, matrix= 64x64, number of slices = 32, slice thickness =3.8, in-plane resolution 3.75x3.75mm, number of repetitions =160 for an 8 minute scanning run. The scan was repeated twice using a different set of novel words for the second scan (stimulus set presentation order was counterbalanced across subjects). The analysis was done in SPM99. Data from each participant were motion corrected, normalized to standard atlas space (ICBM), and spatially smoothed. An event related analysis was used to determine the activation to the novel words relative to the old words and null events. An anatomical mask (including the entire length of the hippocampus, the amygdala, and parahippocampal gyrus) was used to constrain the analysis to the mesial temporal region. The number of activated voxels in each mesial temporal lobe was obtained and a laterality score calculated using the formula (R-L)/(R+L).
RESULTS: The laterality scores between left MTS patients (mean .09; SD .17) and controls (mean -.33, SD .28) differed using a 2-sample t-test (t [9]=2.92, p=.017, two-tailed).
CONCLUSIONS: Mesial temporal lobe activation to novel verbal events separated left MTS patients from controls. This preliminary data suggest that this fMRI procedure may be useful as a diagnostic probe of hippocampal functioning.
Support: Barrow Neurological Foundation