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The effects of the menstrual cycle on cognitive functions were investigated using simple verbal and spatial tasks. Eight healthy young women with a regular, established 28-day menstrual cycle and the occurrence of ovulation on day 14 were tested four times during one cycle. Ten women on non-tricyclic birth control pills were also tested weekly during one cycle. Both groups were matched in age, handedness and education. No significant difference in spatial ability was found but improved verbal working memory, as measured by the verbal span score, was associated with periods of high estrogen levels.
Copyright 2002 Elsevier Science Ltd.
BACKGROUND - Imaging studies have shown disparities in resting metabolism and in functional activation between cognitively normal individuals at high and low risk for AD. A recent study has shown increased parietal activation in high-risk subjects during a paired associates recall task, which the authors postulated might overlap activation typically observed in verbal fluency.
OBJECTIVE - To determine whether parietal activation is altered in a letter fluency task in cognitively normal individuals at high risk for AD.
METHODS - fMRI was used to compare cortical activation between two groups of cognitively normal women differing in their risk for developing AD. A letter fluency task was used, which activates left frontal and parietal regions. The risk groups differed in family history of AD and APOE allele status but were matched in age, education, and measures of cognitive performance. Average age of the study participants was 53 years.
RESULTS - The regional patterns of brain activation were similar between groups and similar to patterns observed by other investigators. However, the high-risk group showed significantly increased activation in the left parietal region despite identical letter fluency performance between risk groups.
CONCLUSIONS - Cognitively normal individuals at high risk for AD show increased brain activation in the left parietal region with letter fluency, a region adjacent to that observed by others using a recall task. This convergence of results indicates disruption of functional circuits involving the left parietal lobe in asymptomatic individuals at increased risk for AD.
Functional magnetic resonance imaging was performed on blind adults resting and reading Braille. The strongest activation was found in primary somatic sensory/motor cortex on both cortical hemispheres. Additional foci of activation were situated in the parietal, temporal, and occipital lobes where visual information is processed in sighted persons. The regions were differentiated most in the correlation of their time courses of activation with resting and reading. Differences in magnitude and expanse of activation were substantially less significant. Among the traditionally visual areas, the strength of correlation was greatest in posterior parietal cortex and moderate in occipitotemporal, lateral occipital, and primary visual cortex. It was low in secondary visual cortex as well as in dorsal and ventral inferior temporal cortex and posterior middle temporal cortex. Visual experience increased the strength of correlation in all regions except dorsal inferior temporal and posterior parietal cortex. The greatest statistically significant increase, i.e., approximately 30%, was in ventral inferior temporal and posterior middle temporal cortex. In these regions, words are analyzed semantically, which may be facilitated by visual experience. In contrast, visual experience resulted in a slight, insignificant diminution of the strength of correlation in dorsal inferior temporal cortex where language is analyzed phonetically. These findings affirm that posterior temporal regions are engaged in the processing of written language. Moreover, they suggest that this function is modified by early visual experience. Furthermore, visual experience significantly strengthened the correlation of activation and Braille reading in occipital regions traditionally involved in the processing of visual features and object recognition suggesting a role for visual imagery.
Copyright 2001 Wiley-Liss, Inc.
Using functional magnetic resonance imaging we examined three important dimensions of attentional control (selective attention, divided attention, and executive function) in 25 neurologically normal, right-handed men and women, using tasks involving the perception and processing of printed words, spoken words, or both. In the context of language-processing manipulations: selective attention resulted in increased activation at left hemisphere parietal sites as well as at inferior frontal sites, divided attention resulted in additional increases in activation at these same left hemisphere sites and was also uniquely associated with increased activation of homologous sites in the right hemisphere, and executive function (measured during a complex task requiring sequential decision-making) resulted in increased activation at frontal sites relative to all other conditions. Our findings provide support for the belief that specific functional aspects of attentional control in language processing involve widely distributed but distinctive cortical systems, with mechanisms associated with the control of perceptual selectivity involving primarily parietal and inferior frontal sites and executive function engaging specific sites in frontal cortex.
Copyright 2001 Academic Press.
This study assessed two relevant aspects of executive dysfunction in children with either Tourette syndrome (TS) or ADHD. Process variables derived from existing neuropsychological measures were used to clarify the executive function construct. Clustering of responses on measures of verbal fluency, figural fluency, and verbal learning was examined to assess strategic response organization. Rule breaks, intrusions, and repetition errors were recorded to assess inhibition errors. No significant differences were found among the three groups (TS, ADHD, and controls) on tasks of response organization (clustering). In our sample, both the ADHD and the TS groups were largely free from executive function impairment, and their performance on the fluency and list learning tasks was in the average range. There was a significant group difference on one of the disinhibition variables, with both TS and ADHD groups showing significantly more intrusions on verbal list learning trials than controls. When more traditional total score variables were analyzed among the three groups, there were no significant differences; however, analysis of effect size revealed medium-to-large effect sizes for Letter Word Fluency total score differences (ADHD vs. controls), and for Semantic Word Fluency total score differences (ADHD vs. TS), with the ADHD group having weaker performance in both comparisons. Results provide some support for the use and analysis of process variables-particularly those related to inhibition and intrusion errors, in addition to the total score variables when assessing executive function deficits in children with ADHD and TS. While group differences may be found, children with uncomplicated TS should not routinely be considered to have significant executive function impairments, and when deficits are found, they may be attributable to other comorbid disorders.
OBJECTIVE - The authors' goal was to evaluate the possibility of treating brain and behavioral aspects of verbal memory dysfunction in patients with schizophrenia through cognitive exercises.
METHOD - Eight patients did daily verbal memory exercises that became progressively more difficult over a 10-week training period. Memory performance and regional brain activations during a verbal memory task were assessed before and after these exercises.
RESULTS - Verbal but not nonverbal memory performance improved after training; three patients made substantial gains, and five showed little change. Performance gains were correlated with increases in task-related activation of the left inferior frontal cortex. One patient given 5 extra weeks of training 6 weeks after the initial training period showed maintenance of initial performance gains 6 weeks after training, further improvement after the second period of training, and normalization of task-related activation of the left inferior frontal cortex.
CONCLUSIONS - Verbal memory deficits can be ameliorated by memory exercises in some patients with schizophrenia. Performance improvements are associated with increased task-related activation of the same brain region that is activated during verbal memory tasks in healthy individuals.
OBJECTIVE - To determine whether brain function is altered in cognitively normal individuals at high risk for AD several years before the typical age at onset for this illness.
BACKGROUND - Neuropathologic alterations in AD precede cognitive impairment by several years. It is unknown whether functional alterations in neural circuitry accompany these neuropathologic changes, and if so, whether they may be detectable before onset of symptoms.
METHODS - We used functional MRI to compare cortical activation between two groups of cognitively normal women differing only in their risk for developing AD. Visual naming and letter fluency tasks were used to activate brain areas subserving object and face recognition, previously described sites of hypometabolism and neuropathologic alteration in AD. The risk groups differed in family history of AD and apolipoprotein E allele status, but were matched in age, education, and measures of cognitive performance. Average age of the study participants was 52 years.
RESULTS - The regional patterns of brain activation were similar between groups. However, the high risk group showed areas of significantly reduced activation in the mid- and posterior inferotemporal regions bilaterally during both tasks despite identical naming and letter fluency performance.
CONCLUSIONS - Cognitively normal individuals at high risk for AD demonstrate decreased brain activation in key areas engaged during naming and fluency tasks. Decreased activation in the high risk group may be a consequence of the presence of subclinical neuropathology in the inferotemporal region or in the inputs to that region. If so, these findings provide evidence of a window of opportunity for disease-modifying treatment before the onset of symptomatic AD.
BACKGROUND - The goal of this study was to model the functional connectivity of the neural systems that subserve attention and impulse control. Proper performance of the Stroop Word-Color Interference Task requires both attention and impulse control.
METHODS - Word-color interference was studied in 34 normal adult subjects using functional magnetic resonance imaging.
RESULTS - Interregional correlation analyses suggested that the anterior cingulate is coupled functionally with multiple regions throughout the cerebrum. A factor analysis of the significant regional activations further emphasized this functional coupling. The cingulate or related mesial frontal cortices loaded on each of the seven factors identified in the factor analysis. Other regions that loaded significantly on these factors have been described previously as belonging to anatomically connected circuits believed to subserve sensory tuning, receptive language, vigilance, working memory, response selection, motor planning, and motor response functions. These seven factors appeared to be oriented topographically within the anterior cingulate, with sensory, working memory, and vigilance functions positioned more rostrally, and response selection, motor planning, and motor response positioned progressively more caudally.
CONCLUSIONS - These findings support a parallel distributed processing model for word-color interference in which portions of the anterior cingulate cortex modify the strengths of multiple neural pathways used to read and name colors. Allocation of attentional resources is thought to modify pathway strengths by reducing cross-talk between information processing modules that subserve the competing demands of reading and color naming. The functional topography of these neural systems observed within the cingulate argues for the presence of multiple attentional subsystems, each contributing to improved task performance. The topography also suggests a role for the cingulate in coordinating and integrating the activity of these multiple attentional subsystems.
O'Boyle and Benbow (1990) have suggested that enhanced involvement of the right hemisphere (RH) during basic information processing is a neuropsychologic characteristic of the gifted brain. To provide converging evidence for this hypothesis, the present study was conducted using a concurrent finger-tapping paradigm. Specifically, 24 mathematically precocious and 16 average ability adolescent males were required to tap a key as quickly as possible while sitting silently (baseline condition), concurrently reading a paragraph aloud (verbal load), or encoding a random form into memory (spatial load). For average ability subjects, the concurrent verbal load reduced tapping rate for the right but not the left hand, reflecting a division of LH resources between linguistic processing of the paragraph and motor control of the contralateral hand. In contrast, for gifted subjects, both their left- and right-hand tapping rates were significantly reduced, suggesting that both hemispheres were engaged during verbal processing. The concurrent spatial task produced a small but reliable reduction in finger-tapping rate for both the left and right hand in each group. These findings provide additional support for the notion that enhanced reliance on RH functioning is a physiological correlate of mathematical precocity in gifted males.