Temporal integration in self-stimulation: a paradox.

Temporal summation of the rewarding effects of medial forebrain stimulation in the rat was investigated by varying the interval separating the two short bursts of stimulation given as a reward in a runway. One finding--that the reinforcing effect of the two bursts is independent of interburst interval--supports a model in which there is perfect summation of the portion of the reward signal that exceeds some threshold. However, the constant-threshold form of this model is not reconcilable with the results of a second experiment, which shows that charge-duration functions obtained with different levels of performance differ by a multiplicative (scalar) factor, that is, the ratio between the values of the two functions is everywhere the same. (The charge-duration function gives the charge required as a function of the train duration.) None of the models of postsynaptic integration so far suggested is capable of explaining simultaneously the fact that the strength-duration function is a perfect hyperbola that has nearly reached its rheobase at a train duration no greater than 2 s, that there is no statistically detectable effect of interburst interval on summation between bursts separated by intervals up to 2 s and longer, and that the strength-duration functions (or, equivalently, the charge-duration functions) derived by using different performance criteria differ by a multiplicative factor.

Characteristics of spatiotemporal integration in the priming and rewarding effects of medial forebrain bundle stimulation.

Only the function relating the required pulse frequency to the interburst interval discriminates between the priming effect and the rewarding effect: Separating two short bursts of pulses has no effect on their combined rewarding effect, but it enhances their priming effect. There are significant nonscalar differences between animals in the number-current and charge-duration functions for priming and reward, but there are no significant differences in these functions between effects within animals. Substantially more electrical-stimulation is required to produce good priming than to produce a reward that sustains maximum possible levels of performance. These findings suggest that the priming effect is a transient excitement generated by the receipt of one or more very large rewards. The discussion elaborates a model that reconciles this hypothesis with the earlier finding that the rewarding effect may be blocked pharmacologically without blocking priming.

Unsupervised waveform classification for multi-neuron recordings: a real-time, software-based system. I. Algorithms and implementation.

We describe a new, mostly software-based device for the sorting of waveforms in an extracellular multi-neuron recording situation. The sorting algorithm is largely unattended, and, after an initial 'learning' process, works in real time. Shape comparisons are based on up to 8 time points in the waveform; these points (the reduced feature set) are chosen automatically by analyzing the current incoming data stream. A feasibility version has been implemented on a LSI-11/2 system, using FORTRAN for set-up calculations and assembler for the real-time operations. Detailed comparisons with performance of other sorting devices are presented in the companion paper.

Use of rabbit serum in the cultivation of Plasmodium falciparum.

Long-term cultivation of four strains of Plasmodium falciparum was achieved in medium with rabbit serum following earlier cultivation of these parasites in medium containing human serum. After a 2- to 3-wk period of adaptation by parasites to their new environment, growth in fresh-frozen rabbit serum was indistinguishable from that observed in human serum. Furthermore, the growth of parasites in medium supplemented with 5% lyophilized serum was similar to that observed when 5 or 10% frozen serum was used. Variability in parasite growth observed with sera obtained from different rabbits could be overcome by the pooling of serum samples. The results suggest that the replacement of human serum by rabbit serum in the cultivation of P. falciparum would be helpful under a number of different circumstances.

Health trends among college freshmen.

Trends in college student health based on an annual survey of college freshmen administered for 30 consecutive years (1966-1995) at colleges and universities nationwide are described. Trends in the following areas are covered: (1) alcohol and drugs, (2) physical health, (3) psychological health, and (4) sexual attitudes. Gender and institutional differences in health behaviors and attitudes among the 1995 class of college freshmen are also considered. Major trends include declines in beer drinking and in physical and emotional self-confidence and an increase in stress and cigarette smoking. "Unhealthy" behaviors and attitudes are reported most often by freshmen at public 2-year institutions.

The institute of medicine's "dietary reference intake" for phosphorus: a critical perspective.

Two questions relevant to the safety of phosphate additives have been raised in the literature: 1) Is the dietary ratio of calcium to phosphorus clinically significant in humans? Specifically, can a high-phosphorus, low-calcium diet cause hypocalcemia and/or secondary hyperparathyroidism in humans? 2) Does the growing use of phosphate-containing food additives increase the risk of low bone density and/or fracture in humans? In 1999, the Institute of Medicine published a monograph which addressed these two questions. This article critically reviews the findings and conclusions of the Institute of Medicine in the light of recent research.

Yohimbine does not affect fat distribution in men.

Forty-seven men with a mean age of 42 years were assigned in random, double-blind fashion to treatment with either placebo or high-dose yohimbine (peak dose, 43 mg/day). Thirty-three subjects completed the six-month program. Variables assessed throughout the study included: body weight and body mass index; total cholesterol and HDL; body fat; and fat distribution as measured both by waist-to-hip ratio and by CT scan. Treatment with yohimbine had no effect on any variable in comparison with the control group.

Pesticide poisoning surveillance through regional poison control centers.

The purpose of this study is to describe pesticide exposure in the population of callers to Minnesota Regional Poison Centers. Case files from 1988 reporting pesticide exposure to humans were identified in cooperation with the Minnesota Center for Health Statistics. Data analysis was conducted by computer using SAS statistical package. Of the 1,428 case files indicating pesticide as the primary substance of exposure to Minnesota residents, a mean age of 5 years (range, one month to 85 years) was identified; 50 percent of all cases were below age 3 years. Males accounted for 1.3 times as many cases as females. Insecticide was identified in the largest percentage of case files (74 percent) followed by herbicide (12 percent), rodenticide (11 percent) and fungicide-nonmedicinal (3 percent). Ingestion was the most common route of exposure; 85 percent of all calls originated from a residence. While insecticides are still the most common types of pesticide call, herbicide has surpassed insecticide in production and sales in the US. In this study, herbicide type exposure calls present a much different picture than other pesticide types. The usefulness of poison control centers for examination of pesticide poisoning is explored. Since reporting occurs coincidental with the exposure and its associated symptoms, each pesticide poisoning report could potentially serve as a true sentinel health event.