The Effect of White Matter Lesions on Intelligence

Brain lesions have long been a topic of interest for neuroscientists, dating in some way back to ancient peoples' practice of trephination, in which holes were created in the skull presumably to alleviate various symptoms and problems. It is also hypothesized that these holes were believed to grant the person special powers. Clearly, in some manner, it has been understood that changes to our heads and brains will produce changes in how our minds work.

A recent study by Bigler, et al (2003) investigated the roles of white matter lesions, Cerebral Atrophy and apolipoprotein-E on cognition in the elderly. This study used a large sample of the elderly population of Cache County, Utah.

A certain kind of white matter abnormality, seen as signal hypertensities on MR scans increase in frequency with age.  Although it is widely understood that a reduction in white matter is correlated with dementia and worsened cognitive processes, the role of white matter lesions (WMLs) has been debated. There have been some studies that supported the argument that Centrum Semiovale White Matter Lesions were the more salient form of brian lesions with respect to intelligence, and some studies that argue for the importance of Peri-Ventricular White Matter Lesions.

In this, and another study (de Groot et al 2000, 2001) periventricular white matter lesions are correlated with impairment in cognitive tasks. The study by Bigler et al (2003) used a battery of CERAD neuropsychological exams, as developed by Welsh et al (1994). Clinical dementia was also evaluated, to create a distinction between the participants with cognitive deficits and those without.

Magnetic Resonance Imaging was used as the exploratory procedure. The researchers calculated total gray and white matter volumes, hippocampal volumes, whole brain volumes, ventricular volumes, and a total ventricle/brain ratio as an index of general atrophy corrected for brain size.

The main result of this study was a solidification of the finding that periventricular white matter lesions are correlated to deficits in cognitive function. PVWMLs were correlated with an r of approximately .30 for almost all cognitive impairments, which included immediate memory, delayed memory, visuospatial skills, language skills, executive function, and a raw intelligence score.