Gina Geffen

Performance measures of 16– to 86-year-old males and females on the auditory verbal learning test

This study reports Auditory Verbal Learning Test (AVLT) data for 153 adults in age groups spanning seven decades, with approximately equal numbers of males and females and matched for intelligence, education, and occupation. Overall performance deteriorated with increased age, females performing better than males. Older subjects recalled fewer words, were more susceptible to information overload during input, showed diminished retrieval efficiency, and had a decline in memory for the source of items. In contrast, rate of learning, forgetting over 20-min, monitoring of recall, and interference effects remained stable across the age range.

Catecholamines and the covert orientation of attention in humans

The role of brain catecholamines in covert orienting was tested in normal subjects using a cued reaction time paradigm which measures the directional engagement, disengagement and movement of attention. Droperidol and clonidine were administered intravenously to suppress central dopamine and noradrenaline transmission. Both drugs produced reductions in the cost of invalid cueing without change in the benefit of valid cueing suggesting that both noradrenaline and dopamine are involved in facilitating the disengagement of attention. These results are relevant to the slowed disengagement observed with parietal lesions in monkeys and humans since this region of the cortex associated with visuospatial analysis receives a dense innervation by both dopamine and noradrenaline projections in primates.

Covert orientation of visual attention in Parkinson's disease: An impairment in the maintenance of attention

Covert orientation of attention was studied in a group of patients with idiopathic Parkinsons disease and compared to a matched control group using a cued reaction time task which measured disengagement, covert movement and engagement of attention. Parkinson patients had an increased response latency and disengaged from attended locations more readily than controls. This impairment in the maintenance of attention in Parkinsons disease was comparable to that produced in a previous study by pharmacological blockade of brain catecholamines in normal subjects. It is suggested that an impairment in the maintenance of oriented attention may underlie some of the cognitive deficits reported in Parkinsons disease.

Genetic influences on handedness: Data from 25,732 Australian and Dutch twin families

Handedness refers to a consistent asymmetry in skill or preferential use between the hands and is related to lateralization within the brain of other functions such as language. Previous twin studies of handedness have yielded inconsistent results resulting from a general lack of statistical power to find significant effects. Here we present analyses from a large international collaborative study of handedness (assessed by writing/drawing or self report) in Australian and Dutch twins and their siblings (54,270 individuals from 25,732 families). Maximum likelihood analyses incorporating the effects of known covariates (sex, year of birth and birth weight) revealed no evidence of hormonal transfer, mirror imaging or twin specific effects. There were also no differences in prevalence between zygosity groups or between twins and their singleton siblings. Consistent with previous meta-analyses, additive genetic effects accounted for about a quarter (23.64%) of the variance (95%CI 20.17, 27.09%) with the remainder accounted for by non-shared environmental influences. The implications of these findings for handedness both as a primary phenotype and as a covariate in linkage and association analyses are discussed.

Interhemispheric control of manual motor activity.

The interhemispheric control of manual motor processes is reviewed, focusing on the clinical evidence from patients with commissurotomies and with agenesis of the corpus callosum. There is little evidence for a role of the corpus callosum in transferring explicit motor commands. Rather, the corpus callosum seems important for transferring lateralised information (such as verbal or visuospatial activity) of the pre-motor variety. Also, the corpus callosum may become very significant when movement begins: there appears to be a transcallosal passage of corollary motor signals and feedback sensory signals that are used to control asychronous bimanual movements and to inhibit the opposite hemisphere from interfering when a simple unimanual movement is required.

Catecholamines and attention I: Animal and clinical studies

One important function of the catecholamine innervation of the cerebral cortex may be the control of attention. Of particular interest are the catecholamine projections to the cerebral cortex from the reticular formation, namely the dopamine neurons of the ventral tegmentum of the midbrain and the noradrenergic neurons of the locus coeruleus in the upper pons. Animal studies implicate noradrenaline and dopamine in a wide range of attention-related behaviours involving search and exploratory activity, distractibility, response rate, discriminability and the switching of attention. Most human studies come from the clinical literature relating to schizophrenia, Parkinsons disease and attention deficit disorder. An association has been claimed in each of these conditions between abnormal catecholamine activity (in particular dopamine) and attentional dysfunction. In particular, difficulty with the attachment of appropriate responses to environmental stimuli, akin to those observed in animals with lesions to central dopamine pathways, indicates a role for dopamine in response selection processes. Overall, the animal and human studies reviewed indicate a role for central noradrenaline and dopamine in the early and late processing of information, respectively.

Genetic Covariance Among Measures of Information Processing Speed, Working Memory, and IQ

The genetic relationship between lower (information processing speed), intermediate (working memory), and higher levels (complex cognitive processes as indexed by IQ) of mental ability was studied in a classical twin design comprising 166 monozygotic and 190 dizygotic twin pairs. Processing speed was measured by a choice reaction time (RT) task (2-, 4-, and 8-choice), working memory by a visual-spatial delayed response task, and IQ by the Multidimensional Aptitude Battery. Multivariate analysis, adjusted for test-retest reliability, showed the presence of a genetic factor influencing all variables and a genetic factor influencing 4- and 8-choice RTs, working memory, and IQ. There were also genetic factors specific to 8-choice RT, working memory, and IQ. The results confirmed a strong relationship between choice RT and IQ (phenotypic correlations: −0.31 to −0.53 in females, −0.32 to −0.56 in males; genotypic correlations: −0.45 to −0.70) and a weaker but significant association between working memory and IQ (phenotypic: 0.26 in females, 0.13 in males; genotypic: 0.34). A significant part of the genetic variance (43%) in IQ was not related to either choice RT or delayed response performance, and may represent higher order cognitive processes.

Functional consequences of the transcallosal removal of intraventricular tumours.

Colloid cysts and other benign tumours of the third and lateral ventricles may be exposed through a small incision in the body of the corpus callosum. This approach is practicable even when ventricular dilatation is slight, and is theoretically less likely to cause epilepsy than the more usual transcortical approach. Disturbances of memory have been noted soon after such operations, but do not cause serious long-term disability. Three patients who underwent transcallosal removal of cysts or tumours some years earlier have been tested by procedures designed to demonstrate interhemispheric transfer of information: they were all found to have defects in transfer of tactile data, but not of information obtained visually. They were not aware of this inability, and do not appear to be inconvenienced by it. The transcallosal route is convenient. The operation sacrifices a functionally significant part of the corpus callosum, but the neurological sequelae have seemed acceptable. However, especially in the elderly, stereoventriculoscopic aspiration may be considered as the initial method of treatment.

The n-back as a dual-task: P300 morphology under divided attention.

The n-back task was hypothesized to be a dual task, permitting the imposition of parametrically increasing attentional and working memory demands, while keeping constant the demands of an embedded matching subtask. Visual targets were presented for 200 ms every 2.2 s at pseudorandomly varying positions on a computer screen. Participants were required to remember the most recent 0, 1, 2, or 3 positions and responded with a choice button push to whether the current target position matched the position presented n items previously. P300 peak latency was constant across n-back tasks, reflecting constant perceptual and cognitive demands of the matching subtask. P300 peak amplitude decreased with increasing memory load, reflecting reallocation of attention and processing capacity away from the matching subtask to working memory activity. These data support a dual-task nature of the n-back, which should be considered when employing this paradigm.

Catecholamines and attention. II: Pharmacological studies in normal humans

Part I of this review [17] found evidence from animal and clinical studies of a role for catecholamines in the control of attention. This part of the review examines the results of a systematic study of the acute effects of a number of catecholamine active drugs on measures of attention in normal adults. The results are interpreted within the context of a general capacity model of information processing in which level of arousal determines the capacity to process stimulus information and level of activation the capacity for processing response demands. Whilst the dopamine antagonist, droperidol, and the alpha agonist, clonidine, had similar effects on behavioural indices of processing capacity and reports of the degree of effort required to carry out processing, they differentially affected subjective state and measures of activation and arousal. These differences provide some support for the hypothesis that central noradrenaline and dopamine modulate the capacity for early and late processing of information, respectively, in humans.