Cognitive change in motor neurone disease : evidence of orbitofrontal dysfunction

Abstract

This study examines the presence of cognitive changes in amyotrophic lateral sclerosis (ALS), a subtype of motor neurone disease. Past research has shown executive dysfunction in patients with ALS and frontotemporal dementia (FTD). A minority of ALS patients without FTD also show some cognitive changes, however the role of the orbitofrontal cortex (OFC) in this patient group has not been investigated. OFC damage can lead to perseveration and behaviour change. The performance of a group of 10 patients with ALS and 10 matched controls was compared on series of cognitive tests known to be sensitive to OFC damage. Two tests of punishment/reward contingency learning were used: the Iowa Gambling Task and our own task based on a previous study of individuals with OFC damage, which requires quickly switching from one rule to a newly learnt rule. A Theory of Mind task known to be sensitive to changes in FTD, the Faux Pas Test was also used. Cognitive tests also included a test of written verbal fluency and a test of confrontation naming ability, as ALS patients have previously shown deficits on these tests. This study did not find any significant group differences, however several patients were outside the normal range of scores for control participants on the three measures sensitive to OFC dysfunction. These results are discussed in relation to relevant research regarding orbitofrontal dysfunction and methodological improvements are suggested. It is concluded that cognitive changes in ALS non dementia can involve orbitofrontal dysfunction and that these changes can occur without concomitant changes affecting written verbal fluency and confrontation naming ability.