Maree Farrow

Increased cortical recruitment in Huntington's disease using a Simon task.

Cognitive deficits in Huntingtons disease (HD) have been attributed to neuronal degeneration within the striatum; however, postmortem and structural imaging studies have revealed more widespread morphological changes. To examine the impact of HD-related changes in regions outside the striatum, we used functional magnetic resonance imaging (fMRI) in HD to examine brain activation patterns using a Simon task that required a button press response to either congruent or incongruent arrow stimuli. Twenty mild to moderate stage HD patients and 17 healthy controls were scanned using a 3T GE scanner. Data analysis involved the use of statistical parametric mapping software with a random effects analysis model to investigate group differences brain activation patterns compared to baseline. HD patients recruited frontal and parietal cortical regions to perform the task, and also showed significantly greater activation, compared to controls, in the caudal anterior cingulate, insula, inferior parietal lobules, superior temporal gyrus bilaterally, right inferior frontal gyrus, right precuneus/superior parietal lobule, left precentral gyrus, and left dorsal premotor cortex. The significantly increased activation in anterior cingulate-frontal-motor-parietal cortex in HD may represent a primary dysfunction due to direct cell loss or damage in cortical regions, and/or a secondary compensatory mechanism of increased cortical recruitment due to primary striatal deficits.

The influence of attention and age on the occurrence of mirror movements

This study utilised a finger force task to investigate the influence of attention and age on the occurrence of motor overflow in the form of mirror movements in neurologically intact adults. Forty right-handed participants were recruited from three age groups: 20-30 years, 40-50 years, and 60-70 years. Participants were required to maintain a target force using both their index and middle fingers, representing 50% of their maximum strength capacity for that hand. Attention was directed to a hand by activating a bone conduction vibrator attached to the small finger of that hand. Based on Cabezas (2002) model of hemispheric asymmetry reduction in older adults, it was hypothesised that mirror movements would increase with age. Furthermore, it was expected that when the attentional demands of the task were increased, motor overflow occurrence would be exacerbated for the older adult group. The results obtained provide support for the model, and qualified support for the hypothesis that increasing the attentional demands of a task results in greater motor overflow. It is proposed that the association between mirror movements and age observed in this study may result from an age-related increase in bihemispheric activation that occurs in older adults, who, unlike younger adults, benefit from bihemispheric processing for task performance.

Motor overflow in Huntington’s disease

We investigated both motor overflow and ability to control voluntary movement in patients with Huntington’s disease (HD). We hypothesised that, compared with controls, overflow would be significantly greater in HD participants and that they would exhibit poorer control of voluntary movement. In a finger flexion task, participants had to maintain target forces representing 25, 50, or 75% of the maximum strength capacity for whichever finger was performing the task; overflow was measured in the corresponding finger of the non-responding hand. HD participants exhibited significantly greater motor overflow than controls, and more difficulty controlling the target force with the active hand. In addition, the degree of overflow in HD participants positively correlated with overall UHDRS motor symptom severity.The presence of exacerbated motor overflow in HD, and its correlation with symptom severity, is an important finding worthy of further investigation.

Progressive Age-Related Changes in the Attentional Blink Paradigm

ABSTRACT Previous studies on aging and attention typically examine group differences between younger and older adults, rather than seeing aging as a continuous process. Using correlational analyses, this study examined progressive changes in the magnitude of the attentional blink (AB) associated with aging. Increased age was found to be significantly associated with the ability to detect the second target (T2), whereby older age was correlated with the production of a longer and more pronounced AB; this supports the proposition that aging is associated with reduced inhibitory processes and selective attention. It was also found that AB performance somewhat improves between ages 18–39 years, but tends to decline from 40 years of age onward, providing an interesting and novel finding that AB effects may become more sensitive at this point in time. The AB task may prove useful in the assessment of selective attention in normal healthy adults, as well as changes associated with pathological aging.

Age-related differences in cognitive function using a global local hierarchical paradigm

While research suggests that normal ageing is associated with compromised divided attentional processing abilities, such studies are comparatively few in comparison to other areas of attention (e.g. selective attention). The current study sought to examine age-related effects in divided attention using a global/local paradigm in three normal healthy age groups: younger adults (20-40 years), middle-aged (40-60 years), and older adults (61-80 years). In three experiments we sought to examine the ability to process local/global stimuli, ability to divide and switch attention, as well as the influence of a cue on target performance. Experiment 1 revealed global precedence and interference for all age groups; older adults were overall significantly slower in their response times. Experiments 2 and 3 suggest an age-related impairment in dividing and switching attention, which may begin as early as middle age. The findings are considered to reflect reduced inhibitory mechanisms, as well as possible neurobiological changes in the normal ageing process.

Attention, inhibition, and proximity to clinical onset in preclinical mutation carriers for Huntington's disease.

Research in preclinical mutation carriers for Huntingtons disease (HD) aims to find measures sensitive to preclinical decline. This study investigated attentional abilities in mutation carriers and noncarriers. Mutation carriers demonstrated a normal “attentional blink” during rapid serial visual presentation, normal covert visual orienting, and normal directing of attention to tactile stimuli. However, they were more likely than noncarriers to make anticipatory responses before target presentation. Additionally, those closer to estimated onset of HD demonstrated larger “inhibition of return” effects. The findings suggest potential changes in cognitive inhibition of unwanted responses, and in automatic inhibition of visual orienting, in preclinical HD.

Motor overflow in schizophrenia

The occurrence of motor dysfunction as a sign of schizophrenia, in addition to being a side effect of medication, has received considerable support in recent years. The current study aimed to systematically investigate both the presence and pattern of one such motor dysfunction, motor overflow. It was hypothesised that patients with schizophrenia would show significantly greater motor overflow than controls, and that the pattern of motor overflow occurrence would also vary significantly between the groups. A finger flexion task was used to examine the presence and pattern of motor overflow. Subjects were asked to maintain target forces, using either their index or small finger, representing 25, 50 or 75% of the maximum strength capacity for whichever finger was performing the task. Patients were found to exhibit significantly greater motor overflow than controls. There were also significant findings with respect to the patterns of motor overflow produced, specifically in regards to fine motor control and performance variability. In summary, patients differed significantly from controls in both the degree and pattern of overflow exhibited.