Angela K. Troyer

Clustering and switching on verbal fluency: the effects of focal frontal- and temporal-lobe lesions

We examined the hypothesis that, on verbal fluency, clustering (i.e. generating words within subcategories) is related to temporal-lobe functioning, whereas switching (i.e. shifting between subcategories) is related to frontal-lobe functioning. Tests of phonemic and semantic fluency were administered to 53 patients with focal frontal-lobe lesions (FL), 23 patients with unilateral temporal-lobe lesions (TL) and 55 matched controls. Performance by FL patients was consistent with our hypothesis: in comparison to controls, patients with left-dorsolateral or superior-medial frontal lesions switched less frequently and produced normal cluster sizes on both phonemic and semantic fluency. Performance by TL patients was not consistent across fluency tasks and provided partial support for our hypothesis. On phonemic fluency, TL patients were unimpaired on both switching and clustering. On semantic fluency, TL patients were impaired on switching in comparison to controls and left TL patients produced smaller clusters than right TL patients. The best indices for discriminating the patient groups, therefore, were phonemic-fluency switching (impaired only with frontal lesions) and semantic-fluency clustering (impaired only with temporal-lobe lesions).

Normative Data for Clustering and Switching on Verbal Fluency Tasks

Normative data for clustering and switching on verbal fluency tasks are provided. Four hundred and eleven healthy adults between the ages of 18 and 91 were given tests of phonemic fluency (FAS or CFL) and semantic fluency (Animals and Supermarket). Raw scores were corrected for demographic (i.e., age, education, and sex) and test (i.e., fluency form) variables that were determined to make sizable contributions to fluency performance. These normative data should be useful for clinicians and researchers in determining the nature of the fluency impairment in any given individual.

Clustering and switching on verbal fluency tests in Alzheimer's and Parkinson's disease

Two components of verbal fluency performance--clustering (i.e., generating words within subcategories) and switching (i.e., shifting between subcategories)--were examined in patients with dementia of the Alzheimer type (DAT), patients with dementia with Parkinsons disease (DPD), nondemented patients with Parkinsons disease (NPD), and demographically matched controls. The DAT and DPD groups were impaired in the number of words generated on both phonemic and semantic fluency. The DAT group produced smaller clusters on both tasks and switched less often on semantic fluency than controls. The DPD group switched less often on both tasks and produced smaller clusters on phonemic fluency than controls. The NPD group was not impaired on any fluency variable. Thus, the total number of words generated on phonemic and semantic fluency did not discriminate the dementia groups from their respective control groups, but measures of clustering and switching did. This differential pattern of performance provides evidence for the potential usefulness of measures of switching and clustering in the assessment of dementia.

Does lateral parietal cortex support episodic memory? Evidence from focal lesion patients

Although neuroimaging and human lesion studies agree that the medial parietal region plays a critical role in episodic memory, many neuroimaging studies have also implicated lateral parietal cortex, leading some researchers to suggest that the lateral region plays a heretofore underappreciated role in episodic memory. Because there are very few extant lesion data on this matter, we examined memory in six cases of focal lateral parietal damage, using both clinical and experimental measures, in which we distinguished between recollection and familiarity. The patients did not have amnesia, but they did show evidence of disrupted recollection on an anterograde memory task. Although the exact mechanisms remain to be elucidated, lateral parietal damage appears to impair some aspects of episodic memory.

Verbal fluency patterns in amnestic mild cognitive impairment are characteristic of Alzheimer's type dementia

Amnestic mild cognitive impairment (aMCI) represents a high-risk factor for Alzheimers disease (AD) and is characterized by a selective decline in episodic memory. Although by definition aMCI is not associated with impaired verbal fluency performance, we examined relative differences between fluency tasks because AD is characterized by poorer semantic than phonemic fluency. Phonemic and semantic fluency trials were administered to 46 healthy controls, 33 patients with aMCI, and 33 patients with AD. Results revealed a progressive advantage (controls > aMCI > AD) in semantic, relative to phonemic fluency. Difference scores between tasks distinguished each group from the others with medium to large effect sizes (d) ranging from 0.49 to 1.07. Semantic fluency relies more on semantic associations between category exemplars than does phonemic fluency. This aMCI fluency pattern reflects degradation of semantic networks demonstrating that initial neuropathology may extend beyond known early changes in hippocampal regions.

Changing everyday memory behaviour in amnestic mild cognitive impairment: A randomised controlled trial

One of the defining differences between mild cognitive impairment (MCI) and dementia is the degree of independence in everyday activities. Effecting memory-related behavioural change in MCI could help maintain daily function and prolong the time before onset of dependency. However, it is well known that changing previously well-established behaviours is difficult to achieve. We conducted a randomised controlled trial to evaluate the effectiveness of a multidisciplinary group-based intervention programme in changing everyday memory behaviour in individuals with amnestic MCI. The intervention provided evidenced-based memory training and lifestyle education to optimise memory behaviour. Fifty-four participants were randomly assigned to treatment or waitlist-control conditions. Consistent with our primary goal, treatment participants showed an increase in memory-strategy knowledge and use from pre-test to immediate post-test, and these gains were maintained at three-month post-test relative to waitlist controls. There were no group differences in memory beliefs or on laboratory tests of objective memory performance. The increase in memory-strategy knowledge and use was associated with the degree of participation in the programme. Individuals with MCI, therefore, can acquire and maintain knowledge about memory strategies and, importantly, can change their everyday memory behaviour by putting this knowledge into practice. This incorporation of practical memory strategies into daily routines could potentially provide the means for maintaining functional independence by individuals with MCI, an issue to be addressed in future research.

Aging and Response Inhibition: Normative Data for the Victoria Stroop Test

ABSTRACT Increased difficulty with response inhibition occurs with age, although there is some controversy as to whether increased interference on Stroop tasks reflects difficulties with response inhibition or simply reflects generalized cognitive slowing. The Victoria Stroop Test (VST) is a brief, easily administered, psychometrically sound version of Stroops original task. Performance on the VST by adults across a wide age span was examined to determine the association between age and various measures of interference. In addition, normative data for the VST were calculated. Participants were 272 healthy, community-dwelling adults age 18 to 94. Age and speed were negatively correlated on all trials of the VST. Importantly, however, interference scores that were corrected for baseline slowing remained highly correlated with age. Similarly, age and error scores on the interference trial were positively correlated, indicating decreased accuracy with age. These findings suggest that increased interference on Stroop tasks with age is not accounted for by simple cognitive slowing and more likely reflects other cognitive changes, such as decreased response inhibition. The VST has a number of administrative and psychometric strengths, and the provision of normative data should enhance its potential for clinical and research applications.

Source memory and divided attention: reciprocal costs to primary and secondary tasks.

Source memory, in comparison with item memory, is more sensitive to frontal lesions and may require more strategic processing. Divided attention was used to restrict attentional resources and strategic processing on memory tasks. Participants encoded and retrieved items (i.e., words) and source (i.e., voice or spatial location) while concurrently performing a finger-tapping (FT) or visual reaction-time (VRT) task. Memory accuracy costs under divided attention were greater for retrieval of source than item and were greater with VRT than FT. Similarly, costs to the secondary task were greater when concurrently retrieving source as opposed to item and were greater for VRT than FT. Effects were stronger when spatial location was used as the source task. Findings support the idea that processing source information requires more attentional resources and effort than processing item information. Furthermore, concurrent performance of VRT produced greater interference with a task that was more dependent on intact frontal functioning and better simulated the performance of patients with frontal dysfunction.

Chronic obstructive pulmonary disease: Effects of hypoxia on neurological and neuropsychological measures

Eighteen patients with chronic obstructive pulmonary disease (COPD) were administered a series of pulmonary, neurological, and neuropsychological measures to test if there was an effect of COPD on neurological and cognitive functioning. Overall, there was no evidence of general dementia in this sample. Measures of immediate and delayed memory, complex attention, and speed of information processing correlated highly with arterial carbon dioxide partial pressure and, to a lesser extent, with oxygen partial pressure. Measures of language abilities, perceptual-motor functioning, and simple attention generally were not related to arterial gas pressures. A similar pattern of findings was obtained when group differences were examined between participants classified as severely hypoxic or mildly hypoxic, although group differences were mitigated by premorbid IQ differences. Hypoxia in COPD results in a relatively focused pattern of impairment in measures of memory function and tasks requiring attention allocation. The memory dysfunction may be related to involvement of limbic memory regions necessary for explicit memory. The attentional deficits were attributed to diffuse brain involvement resulting in reduced resource allocation. Early diagnosis and treatment of the hypoxia is essential.

Episodic, but not semantic, autobiographical memory is reduced in amnestic mild cognitive impairment

Amnestic mild cognitive impairment (aMCI) is characterized by decline in anterograde memory as measured by the ability to learn and remember new information. We investigated whether retrograde memory for autobiographical information was affected by aMCI. Eighteen control (age 66-84 years) and 17 aMCI (age 66-84 years) participants described a personal event from each of the five periods across the lifespan. These events were transcribed and scored according to procedures that separate episodic (specific happenings) from semantic (general knowledge) elements of autobiographical memory. Although both groups generated protocols of similar length, the composition of autobiographical recall differentiated the groups. The aMCI group protocols were characterized by reduced episodic and increased semantic information relative to the control group. Both groups showed a similar pattern of recall across time periods, with no evidence that the aMCI group had more difficulty recalling recent, rather than remote, life events. These results indicate that episodic and semantic autobiographical memories are differentially affected by the early brain changes associated with aMCI. Reduced autobiographical episodic memories in aMCI may be the result of medial temporal lobe dysfunction, consistent with multiple trace theory, or alternatively, could be related to dysfunction of a wider related network of neocortical structures. In contrast, the preservation of autobiographical semantic memories in aMCI suggests neural systems, such as lateral temporal cortex, that support these memories, may remain relatively intact.