The biological efficacy of the transfer function

The most popular neural network strategy is back propagation. This strategy initiated general interest in neural networks among researchers. While back propagation can solve nonlinear problems, it is considered to be a poor example of neuron functioning. Recently, Gardner (1993) has made a strong case for a back propagating phenomenon in networks of living neurons. In this paper, we present a few simple computational examples that investigate another component of the typical back propagation network. The effects of varying transfer functions are illustrated along with the resulting variations in possible synaptic weights. Graphic presentations in 3-D space of the relationship between transfer functions and synaptic weights suggest neural analogies of cell-firing rate and network control.     

Increased regional cerebral glucose metabolism and semantic memory performance in Alzheimer's disease: A pilot double blind transdermal nicotine positron emission tomography study

Nicotinic receptor dysfunction and impaired semantic memory occur early in Alzheimer's disease patients (AD). Previous research implied that nicotine's ability to enhance alertness, arousal, and cognition in a number of nonclinical populations was a function of its ability to stimulate CNS nicotinic cholinergic receptors. In this study it was hypothesized that transdermal administration of nicotine would increase both regional cerebral glucose metabolism (rCMRglc) and semantic memory (as assessed by verbal fluency). Two mild AD and two elderly controls underwent positron emission tomography scanning during a double blind nicotinic agonist verbal fluency challenge procedure. rCMRglc increases occurred in both AD patients, but not controls. In the two AD patients, verbal fluency scores increased by an average of 17%. One elderly control's verbal fluency increased, and the other decreased. These findings suggest that nicotine's effect on metabolism and verbal fluency is due to its ability to stimulate the cholinergic system.     

Prediction of school attendance problems

Predictions of school attendance problems were made for 262 14-yr-old school children on the basis of intelligence, social class and personality (extraversion-introversion) differences. The overall success of prediction was highly significant, though this was achieved largely by one school group alone. The results are discussed in terms of future early identification and therefore prevention of problems.     

An automated trainer for improving visual acuity in myopic adults

Several studies have found training procedures derived from the experimental analysis of behavior to result in improved visual acuity for myopic adults. The present paper describes an automated trainer that incorporates critical training components and eliminates excessive time demands of the fading and feedback procedures reported in the literature. Implications for standardization and long-term training are discussed.     

Sensitivity to shifts of a point stimulus: An instance of tactile hyperacuity

The sensitivity of the tactile sense to shifts in the position of a point stimulus was determined at four body loci: the index finger, forehead, belly, and back. Water-jet stimulation was used, a method which allows frictionless travel of a point stimulus over the skin. Three subjects were tested by means of the method of forced choice, with the task being to say whether the stimulus moved to the right or to the left. The shift threshold was defined as that shift excursion which gave rise to 75% correct responding. The basic finding was that shift thresholds were on the order of 10 to 30 times smaller than the corresponding two-point limens obtained by Weinstein (1968) for the same body loci. These unexpectedly small shift thresholds indicate an exquisite sensitivity of the cutaneous sense to rapid changes in position of a point stimulus. A physiological model is presented which accounts for the difference between localization and spatial resolution. nt]mis|This research was supported by Department of Health~ Education, and Welfare Grant 14-P-SS282/9 from the Social and Rehabilitation Services, NIH Research Grant R01-EY-00686 from the National Eye Institute, and the Smith-Kettlewell Eye Research Foundation.     

Behavioral training for myopia: long term maintenance of improved acuity

Two female myopic students participated in a behavioral training program designed to improve uncorrected visual acuity. Following a 3-day baseline, each subject underwent 12 days of training involving stimulus fading and feedback. Acuity measures were taken daily during baseline and training phases and weekly for more than 2 months following the termination of training. Both subjects showed improved acuity as a function of the training program and this improvement was maintained throughout the follow-up period. The results are discussed with respect to the growing body of research evaluating behavioral training for myopia.     

A nonobtrusive heart rate telemetry system for rats

A harness for recording heart rate (HR) from unrestrained rats and an inexpensive FM transmitter for broadcasting high-resolution EKGs are described. The harness, which employs surface electrodes rather than skin pins or implanted electrodes, is especially valuable for recording HR over extended periods of time. Because it is comparatively free of noise generated by the animal’s activity, the system is applicable to a wide range of experimental conditions. Sample HRs obtained from three strains of rats while engaging in different behavioral categories are presented.