Effect of current on the maximum possible reward.

Using a 2-lever choice paradigm with concurrent variable interval schedules of reward, it was found that when pulse frequency is increased, the preference-determining rewarding effect of 0.5-s trains of brief cathodal pulses delivered to the medial forebrain bundle of the rat saturates (stops increasing) at values ranging from 200 to 631 pulses/s (pps). Raising the current lowered the saturation frequency, which confirms earlier, more extensive findings showing that the rewarding effect of short trains saturates at pulse frequencies that vary from less than 100 pps to more than 800 pps, depending on the current. It was also found that the maximum possible reward--the magnitude of the reward at or beyond the saturation pulse frequency--increases with increasing current. Thus, increasing the current reduces the saturation frequency but increases the subjective magnitude of the maximum possible reward.     

Normative Symbol Digit Modalities Test performance in a community-based sample.

The Symbol Digit Modalities Test is a substitution task that is the inverse of the Digit Symbol Test. The familiar task of filling numbers in boxes, and the availability of an oral administration, make this a popular screening instrument for brain impairment. Normative data were previously reported for a variety of clinical groups, but complete information on non-clinical samples across age, education, gender, and socioeconomic status is limited. The present study examines the performance of a community-dwelling control sample across age, education, gender, and income groupings. In a multivariate model, these four variables did not impact test performance. These results support the utilization of the SDMT as a robust screening test for adult neuropsychological impairment.     

CT diagnostic features of Alzheimer disease: importance of the choroidal/hippocampal fissure complex

Neuropathologic changes in the temporal lobe, including focal atrophy of the subiculum and entorhinal cortex, have been described in association with Alzheimer disease. We studied the usefulness of detecting temporal-lobe structural changes on CT in making the diagnosis of Alzheimer disease. The dementia imaging protocol we use includes thin-section (5 mm) cuts of the temporal lobe oriented 20 degrees negative (caudal) to the plane of the canthomeatal line. Thirty-four patients with suspected Alzheimer disease and 20 normal elderly control subjects, all between 65 and 80 years old, were studied with a standard protocol that also included neurologic and medical examinations and detailed psychometric testing. All the temporal-lobe evaluations of the five variables measured were significantly associated with the presence or absence of Alzheimer disease. Almost all Alzheimer patients showed evidence of mild or greater severity of overall temporal-lobe atrophy. The absence of temporal-lobe atrophy, seen in approximately one half the normal cases, identified normal individuals with a high degree of specificity (95%). The presence of characteristic hippocampal lucency, apparently due to enlargement of the choroid and hippocampal fissures, showed the highest sensitivity and classification accuracy of all the variables tested (82 and 80% respectively; p less than .001), correctly identifying 82% of Alzheimer patients and 80% of Alzheimer patients and control subjects. These results indicate that CT detection of structural changes in the temporal lobe and hippocampus strongly support the diagnosis of Alzheimer disease. A temporal-lobe imaging protocol for CT, and by extension for MR, is suggested for the evaluation of patients with the clinical diagnosis of a dementing disorder.     

Intravascular ultrasonography: validation studies and preliminary intraoperative observations

Intravascular ultrasonography is emerging as an important imaging modality to assess the presence, distribution, and extent of atherosclerotic vascular disease. To determine the accuracy and clinical utility of intravascular ultrasonography, a flexible catheter-based system was used to generate two-dimensional, cross-sectional vascular images. In 23 arteries of 11 sheep 206 in vivo images demonstrated an echo-free lumen surrounded by three distinct concentric acoustic transitions corresponding to intima, media, and adventitia. Ultrasound measurements of lumen diameter and area correlated significantly with those of corresponding arteriographic measurements obtained by use of digital calipers (r = 0.91, r = 0.86). To evaluate clinical feasibility, intraoperative images (n = 160) were obtained in 10 patients undergoing vascular bypass or hemodialysis access procedures. The images depicted luminal configuration and arterial wall morphologic characteristics. Measurements of lumen diameter and lumen area correlated closely with corresponding intraoperative arteriography (r = 0.81, r = 0.79). The ultrasound images demonstrated arterial stenoses, intimal hyperplasia, intraluminal thrombus, polytetrafluoroethylene graft material, and anastomotic sites. We conclude that flexible catheter-based ultrasonography produces images that accurately demonstrate arterial wall architecture, lumen diameter, and area. Intraoperative application can produce images that provide unique information thus expanding the clinical potential of ultrasonography as a guidance system for vascular procedures.     

EMG biofeedback for handwriting disabilities: a critical examination of the literature

A critical examination of the literature on the use of electromyographic (EMG) biofeedback for problems of handwriting is presented. Examined are the procedures, results and conclusions of clinical treatments of writer's cramp and the habilitation of writing. The major flaws in each study are discussed and conclusions drawn from the review are presented, the primary one being that EMG biofeedback of the muscles of the upper extremity has yet to be demonstrated as a treatment of choice for handwriting disabilities. The lack of a sound foundation of data is seen as the main reason for the paucity of investigations in this particular area. Suggestions for further work are offered.