Mark Jacobson

Architecture of selected muscles of the arm and forearm: anatomy and implications for tendon transfer.

The architectural features of twenty-one different forearm muscles (n = 154 total muscles) were studied. Muscles included the extensor digitorum communis to the index, middle, ring, and small fingers, the extensor digit quinti, the extensor indicis proprius, the extensor pollicis longus, the flexor digitorum superficialis, the flexor digitorum profundus, the flexor pollicis longus, the pronator quadratus, the palmaris longus, the pronator teres, and the brachioradialis. Muscle length, mass, fiber pennation angle, fiber length, and sarcomere length were determined with the use of laser diffraction techniques. From these values, physiologic cross-sectional area and fiber length/muscle length ratio were calculated. The individual digital extensor muscles were found to be relatively similar in architectural structure. Similarly, the deep and superficial digital flexors were very similar architecturally, with the exception of the small finger flexor digitorum superficialis, which was much smaller and shorter than the rest of the digital flexors. The brachioradialis and the pronator teres had dramatically different architectural properties. While the masses of the two muscles were nearly identical, the muscles had significantly different predicted contractile properties based on their different fiber arrangement. The brachioradialis, with its long fibers arranged at a small pennation angle, had a physiologic cross-sectional area that was only one third that of the pronator teres, with its short fibers that were more highly pennated. Using these architectural data and the statistical method of discriminant analysis, we provide additional information that might be useful in the selection of potential donor muscles to restore thumb flexion, thumb extension, finger extension, and finger flexion.

Architectural design of the human intrinsic hand muscles

The architectural features of twenty different muscles (18 intrinsics and 2 thumb extrinsics, n = 180 total muscles) were studied. Muscle length, mass, fiber pennation angle, fiber length, and sarcomere length were determined. From these values, physiologic cross-sectional area and fiber length/muscle length ratio were calculated. Intrinsic muscle lengths were relatively similar to one another, which we interpreted as representing a space constraint within the hand. However, several specialized architectural designs were observed: lumbrical muscles had an extremely high fiber length/muscle length ratio, implying a design toward high excursion. The first dorsal interosseous and adductor pollicis had physiologic cross-sectional areas comparable to those of extrinsic muscles and much greater than those of the other intrinsic muscles. The interosseous muscles had relatively high physiologic cross-sectional areas with low fiber length/muscle length ratios, suggesting their adaptation for high force production and low excursion. Taken together, these observations illustrate the underlying structural basis for the functional capacities of the intrinsic muscles.

The myth of testing construct validity using factor analysis or correlations with normal or mixed clinical populations: Lessons from memory assessment

For nearly a century, the primary method employed by psychologists to define and test the validity of constructs evaluated by assessment instruments has been shared-variance techniques such as intervariable correlations or factor analysis with large normative or mixed clinical samples. To illustrate the shortcomings of this approach, we conducted (1) correlational analyses of immediate- and delayed-memory measures separately in normal participants and in homogeneous samples of patients with either Alzheimers disease or Huntingtons disease; and (2) factor analysis of immediate and delayed-recall and recognition measures in a large, homogeneous sample of patients with Alzheimers disease. The findings revealed that cognitive measures that share variance in the intact brain-thereby giving the facade of assessing a unitary construct-can dissociate and contribute to unique variance in the damaged brain, but only if the pathology occurs in brain regions known to disrupt vital cognitive processes tapped by those measures. The results illustrate that shared-variance procedures applied to normal or mixed clinical populations can mask some of the most vital cognitive constructs, such as the classic distinction between short- and long-term memory. Implications of these findings for research and clinical practice are discussed.

Muscle Functional Deficits After Tourniquet Ischemia

The contractile properties of the rabbit tibialis anterior muscle were studied 48 hours after an ischemic episode induced by pneumatic tourniquet compression of the thigh. Forty animals were divided into five groups, each of which had continuous ischemia of either 1, 2, or 4 hours, or a total of 2 or 4 hours of ischemia interrupted by 10 minutes of reperfusion at 1-hour intervals. Con tralateral limbs served as controls. Muscle contractile properties were tested by stimulation of the peroneal nerve distal to the site of tourniquet compression. Peak tetanic tension in the 1-hour group did not differ signifi cantly from controls. In the 2- and 4-hour groups, peak tetanic tensions were 31 % and 2% of controls, respec tively, and twitch tensions were 25% and 1 % of controls, respectively. Hourly reperfusion intervals had no sig nificant effect on maximum tetanic or twitch tension compared with continuous ischemia for either 2 or 4 hours. Clinically significant muscle dysfunction may be in duced by 2 or more hours of pneumatic tourniquet ap plication. Hourly reperfusion intervals may not improve skeletal muscle function distal to the tourniquet. How ever, reperfusion intervals could still affect muscle that is compressed beneath the cuff. Tourniquet-induced contractile deficits may interfere with postoperative functional recovery.

A comparison of two brief screening measures of cognitive impairment in Huntington's disease.

The goal of this study was to explore whether the Montreal Cognitive Assessment (MoCA), a new screening instrument, would be more sensitive to mild to moderate cognitive impairment in Huntingtons disease (HD) than an established screening measure, the Mini Mental State Exam (MMSE). Our reasoning for this query is that the MoCA includes a broader range of test items and an additional assessment of executive functioning and attention compared with the MMSE. Using the receiver operating characteristic (ROC) analysis to examine performance of HD and control groups on both tests on overall scores and scores from various subdomains (i.e., visuospatial abilities) revealed that the MoCA achieved higher sensitivity without sacrificing specificity in many domains relative to the MMSE.

Creativity Lost: The Importance of Testing Higher-Level Executive Functions in School-Age Children and Adolescents

In school settings, students are typically evaluated using group achievement tests, IQ scales, and college entrance exams that focus more on rote-verbal skills (e.g., vocabulary, mathematical facts) than on higher level executive functions (e.g., abstract thinking, problem solving). However, recent neuropsychological findings suggest that rote-knowledge skills and executive functions are divergent cognitive domains that can be dissociated in both adults with frontal lesions and children with neurodevelopmental disorders. New correlational findings obtained from 470 children and adolescents provide additional support for the divergent nature of these cognitive domains and the existence of subgroups of students who exhibit either strengths in abstract, creative thinking with relative weaknesses in rote-verbal skills or vice versa. The results suggest that current school assessment practices may result in academic roadblocks for those students who have strengths in abstract, creative thinking but whose relative weaknesses in rote-verbal skills may hinder their ability to take college entrance exams.

Impairments in source memory for olfactory and visual stimuli in preclinical and clinical stages of Huntington's disease

Individuals in preclinical and clinical stages of Huntingtons disease (HD) demonstrate impairments in olfactory functioning. In addition, HD patients are impaired in source memory for verbal stimuli. A task combining both source and odor memory may be particularly sensitive to early changes in HD. The present study examined source and item memory for olfactory and visual stimuli in 10 individuals with HD, 10 asymptomatic HD gene carriers, 8 nongene carriers who had a parent with HD, and 20 normal controls. During the study phase, a male and a female experimenter (sources) presented odors and objects to the participant in an alternating sequence. To assess item memory, a stimulus from the study phase (target) and a novel stimulus (distractor) were presented, and the participant was asked to choose the target. To assess source memory, the experimenter presented a stimulus and asked whether the male or female experimenter had previously presented the stimulus. Results indicate that source memory for both visual and olfactory stimuli was impaired in HD patients compared to normal controls. In asymptomatic gene carriers, however, source memory for olfactory stimuli, but not visual stimuli, was more impaired than in nongene carriers and normal controls. Furthermore, gene carriers and HD patients showed a similar degree of impairment in source memory for olfactory stimuli. The only significant impairment found in item memory was for olfactory stimuli in HD patients. These results suggest that source memory for olfactory stimuli may be particularly sensitive to neuropathological changes in preclinical stages of HD.

Behavioral Measures of Saccade Latency and Inhibition in Manifest and Premanifest Huntington's Disease

ABSTRACT Initiation and inhibition of saccadic eye movements has been shown to be impaired in patients with Huntingtons disease (HD) and premanifest gene carriers (PMGC), and may provide biomarkers useful in tracking phenotypic change. Computerized behavioral tests of prosaccade latency and disinhibition presented to 31 non–gene carriers (NGC), 25 PMGC, and 12 HD patients. These tests provided quantitative performance measures without use of eye-tracking equipment. Significant differences on saccade tests were found, with PMGC intermediate between NGC and HD patients. Saccade latency discriminated PMGC from NGC, whereas saccade disinhibition discriminated PMGC from HD patients. Results suggest utility of behavioral saccade measures as premanifest indicators of phenoconversion in HD.

Do subgroups of patients with Alzheimer's disease exhibit asymmetric deficits on memory tests?

Several studies have reported asymmetric cognitive profiles in patients with Alzheimers disease (AD), but these results have almost exclusively been found using non-memory cognitive instruments. The present study investigated whether AD patients who display lateralized profiles on non-memory cognitive instruments also exhibit asymmetric deficits on verbal versus spatial memory tests. Sixty-eight AD patients participated in the study: 36 with a High Verbal cognitive profile, and 32 with a High Spatial profile. The results indicated that the High Verbal AD patients performed significantly better than the High Spatial AD patients on verbal memory tests, but the two subgroups failed to differ on spatial memory tests. Implications of these findings for understanding the heterogeneous nature of cognitive profiles in AD patients are discussed.

Olfactory and auditory event-related potentials in Huntington's disease.

The influence of Huntingtons disease (HD) on the olfactory event-related potential (OERP), an electrophysiological measure of olfactory information processing, has not been reported to date. In the present study, olfactory and auditory event-related potentials (ERPs) were recorded monopolarly from Fz, Cz, and Pz electrode sites in 8 patients with HD and 8 age- and gender-matched control participants. Results demonstrated that individuals with HD were delayed compared with controls on the P3 component of the OERP (p<.001), with a trend toward a significant delay on the auditory ERP P3 (p<.06). The effect size for OERP P3 latency (pi(2)=.72) was larger than that for the auditory P3 (pi(2)=.24), which has previously been shown to be delayed in HD. Patients performed significantly worse than controls did on all neuropsychological measures. These measures significantly correlated with several components of the OERP. These findings extend the understanding of olfactory deficits in HD.