White matter microstructure complements morphometry for predicting verbal memory in epilepsy

• Published in: Cortex 2014-09, Vol.58, p.139-150
• Main Authors: McDonald, Carrie R., Leyden, Kelly M., Hagler, Donald J., Kucukboyaci, Nuri E., Kemmotsu, Nobuko, Tecoma, Evelyn S., Iragui, Vicente J.
• Format: Article
• Language: English
• Subjects: Adult; Adult and adolescent clinical studies; Biological and medical sciences; Cortical thickness; Diffusion Tensor Imaging; Epilepsy, Temporal Lobe - pathology; Epilepsy, Temporal Lobe - psychology; Female; Headache. Facial pains. Syncopes. Epilepsia. Intracranial hypertension. Brain oedema. Cerebral palsy; Humans; Magnetic Resonance Imaging; Male; Medical sciences; Memory - physiology; Memory, Episodic; Middle Aged; Nervous system (semeiology, syndromes); Neurology; Neuropsychological Tests; Organic mental disorders. Neuropsychology; Psychology. Psychoanalysis. Psychiatry; Psychopathology. Psychiatry; Temporal Lobe - pathology; Temporal lobe epilepsy; Verbal Learning - physiology; Verbal memory; Volumetric imaging; White Matter - pathology; Young Adult
• ISSN: 0010-9452; 1973-8102
• DOI: 10.1016/j.cortex.2014.05.014

Verbal memory is the most commonly impaired cognitive domain in patients with temporal lobe epilepsy (TLE). Although damage to the hippocampus and adjacent temporal lobe structures is known to contribute to memory impairment, little is known of the relative contributions of white versus gray matter structures, or whether microstructural versus morphometric measures of temporal lobe pathology are stronger predictors of impairment. We evaluate whether measures of temporal lobe pathology derived from diffusion tensor imaging (DTI; microstructural) versus structural MRI (sMRI; morphometric) contribute the most to memory performances in TLE, after controlling for hippocampal volume (HCV). DTI and sMRI were performed on 26 patients with TLE and 35 controls. Verbal memory was measured with the Logical Memory (LM) subtest of the Wechsler Memory Scale–III. Hierarchical regression analyses were performed to examine unique contributions of DTI and sMRI measures to verbal memory with HCV entered in block 1. In patients, impaired recall was associated with increased mean diffusivity (MD) of multiple fiber tracts that project through the temporal lobes. In addition, increased MD of the left cortical and bilateral pericortical white matter was associated with impaired recall. After controlling for left HCV, only microstructural measures of white matter pathology contributed to verbal recall. The best predictive model included left HCV and MD of the left inferior longitudinal fasciculus (ILF) and pericortical white matter beneath the left entorhinal cortex. This model explained 60% of the variance in delayed recall and revealed that MD of the left ILF was the strongest predictor. These data reveal that white matter microstructure within the temporal lobe can be used in conjunction with left HCV to enhance the prediction of verbal memory impairment, and speak to the complementary nature of DTI and sMRI for understanding cognitive dysfunction in epilepsy and possibly other memory disorders.