Verbal fluency and executive dysfunction in amyotrophic lateral sclerosis (ALS)

Area of Science:

• Neuropsychology
• Neurology
• Cognitive Science

Background:

• Amyotrophic lateral sclerosis (ALS) is associated with cognitive deficits, particularly executive dysfunction.
• Verbal fluency tests consistently reveal impairments in ALS patients, but underlying causes are debated.
• Previous studies often lack controls for motor speed, potentially exaggerating cognitive deficits.

Purpose of the Study:

• To investigate the specific cognitive processes underlying verbal fluency deficits in ALS patients.
• To differentiate between executive dysfunction, phonological loop function, and word retrieval impairments.
• To assess the impact of motor speed on cognitive test performance in ALS.

Main Methods:

• Compared 22 ALS patients and 25 healthy controls using a battery of cognitive tests.
• Assessed intrinsic response generation (verbal and design fluency), phonological loop functions (Phonological Similarities and Word Length Effects), and word retrieval (naming, sentence completion).
• Included tests designed to control for motor speed and patient disability levels.

Main Results:

• ALS patients showed significant impairments in intrinsic response generation (Written Verbal Fluency, Category Fluency, Design Fluency).
• Phonological loop functions were intact, but working memory capacity was significantly reduced in ALS patients.
• No deficits were observed in simple word retrieval tasks.

Conclusions:

• Verbal fluency deficits in ALS stem from higher-order executive dysfunction, likely involving the supervisory attentional system or central executive component of working memory.
• Impairments are not due to phonological loop dysfunction or primary linguistic deficits.
• Controlling for motor speed is crucial for accurate assessment of cognitive function in ALS.