Central auditory and visual processing in Huntington's disease.(Report)

Central auditory and visual processing was examined in 9 persons with confirmed Huntington's disease (HD), 9 age-matched controls (A-MC), and 17 younger controls (YC) during text-word (TWV) and picture-word (PWV) verification tasks. Participants were presented with an orthographic representation or picture of a common noun word on a computer screen, while simultaneously hearing a spoken word through headphones. Participants were instructed to indicate whether the spoken word matched the picture or written word. Within-group comparisons revealed that, in the HD and A-MC groups, response time of the PWV task was significantly longer than that of the TWV task; there was no difference observed in response accuracy for any of the groups. The HD group was not significantly different than the A-MC group in between-group comparisons of the difference response time (PWV response time minus TWV response time). Statistical significance was reached when the HD group was compared to the YC group. Comparison of the mean response accuracy between groups revealed there was not a statistically significant difference when comparing the HD and the A-MC groups, but there was statistical significance between the HD and YC groups. Finally, a strong, negative correlation was found between the Dementia Rating Scale-2 (DRS-2; Mattis, 2001) performance and PWV response time in the HD group.

INTRODUCTION

Huntington's disease (HD) is an autosomal dominant neurodegenerative genetic disorder. Disease onset typically occurs between the ages of 35 and 45 years, although it has been observed in children as young 2 years of age and in adults as late as the eighth decade of life (Myers et al., 1991; Young et al., 1986). Neuroanatomical changes in HD include atrophy of the caudate nucleus and putamen in the striatum of the basal ganglia. The loss of connections between striatal neurons in these regions may affect structure and function of some frontal lobe regions (Vonsattel et al., 1985).

HD is characterized by progressive decline in motoric and cognitive function. Motoric changes that may include chorea, dystonia, bradykinesia, rigidity, gait disorder, or motor impersistence occur in involuntary and voluntary movements (Young et al., 1986). Attention, memory, visual-motor, visual-graphic abilities, and executive functions are frequently impaired in persons with HD (Barquero-Jimenez & Gomez-Tortosa, 2001).

Disturbances of speech and language are typically observed in this population. The most frequently observed speech problems are those affecting the intelligibility of speech, such as dysarthria and dysprosodia (Darley, Aronson, & Brown, 1975). Multiple language changes can occur in syntactic complexity (Gordon & Illes, 1987; Illes, 1989; Murray, 2000; Podoll, Caspary, Lange, & Noth, 1988), in confrontation naming (Hodges, Salmon, & Butters, 1990), and in semantic retrieval (Ho et al., 2002; Martin & Fedio, 1983). Two processing modes related to communicative function are auditory processing (AP) and visual processing (VP). These processes affect the ability to connect external information sets to the individual's cognitive and semantic resources.

Stach, Spretnjak, and Jerger (1990) reported that individuals with neurodegenerative diseases frequently demonstrate dysfunction in central auditory processing (CAP) independent of peripheral hearing capacity. HD caused atrophy of neural fibers within the basal ganglia, and neural fibers of the CANS traveling near the basal ganglia have been functionally impaired as a result of this atrophy. Therefore, investigations of CAP impairment in persons with HD recently have drawn attention. Homberg et al. (1986) reported that persons with HD presented with abnormal latency responses during an event-related evoked potential paradigm; however, other studies contradict this report (Ehle, Stewart, Lellelid, & Leventhal, 1984; Lawson, Barrett, Kriss, & Halliday, 1984).

In behavioral tests of CAP, Bradham (1998) utilized a synthetic sentence identification task with a competing message, a dichotic digits task, and a duration pattern task with three groups of participants: those with HD, those gene positive but presymptomatic for HD, and control participants. It was determined that participants with HD scored significantly poorer than controls on seven of the nine CAP tasks administered. No differences were observed between those identified as pre-symptomatic and their controls. Results of this investigation suggest that the CANS are impaired in HD, but may not be observable until the gene positive patient is symptomatic for the disease.