Paper 2: Electrical Brain Stimulation Reward:
Effects of Food Deprivation
What places psychology squarely among the “hard” sciences is the complexity of measurement of the behavioral phenomena using physiological methods. This approach is a fundamental area of psychology and a founding body of research in the very popular field in neuroscience research. Prominent in the research in physiological psychology is the study of drives (especially hunger), learning (especially Pavlovian and operant conditioning), and emotion (especially positive reinforcement or reward). The experiment that follows involves all three areas. We will explore the effects of manipulating the hunger drive on operant performance for electrical brain stimulation reward. The research we will perform for this lab is a demonstration of the effects of food deprivation on reward mechanism in a brain site that has been found to influence food intake. The region is the lateral hypothalamus (LH) and has been shown to increase food intake when stimulated (both with mild electrical stimulation and chemical stimulation). Classic research has shown that electrical stimulation of the LH will also serve as reinforcement for operant conditioning. The operant response we will be exploring is lever or bar pressing in an operant chamber (or “Skinner box”). The use of the operant chamber is a useful way to explore the important aspects of operant conditioning. Performance in the chamber is and has been shown over and over again to explain and predict operant and classical conditioning of humans and other species.
The issue that we will explore is the effects of food deprivation on pleasurable sensations in the brain. Many researchers have used psychophysical methods to explore the reward effects of brain stimulation in various brain regions. In our experiment, you will be given raw data of performance of albino rats trained to lever-press for brain stimulation reward (BSR), brief pulses of electricity in the LH. A key piece of the research is that the LH appears to be a key brain area in controlling food intake. Researchers in my lab collected the data that you will be given in this experiment. You should write the report as though you actually performed the operations in the rat experiment.
This is an opportunity to explore experimentation in the hard science aspect of psychology. Research of this type has been of great value in understanding the physiological mechanisms that mediate behavior. While the experiments on brain stimulation reward (BSR) were completed some time ago, the research questions, BSR methods, and operant procedures are currently used and relevant to cutting-edge experimentation in the neurosciences.
Subjects [not participants]. Sprague-Dawley albino rats were maintained on ad libitum (ad Lib.) food and water except for the food deprivation condition when only water was available. The animals were maintained under a 12:12 light-dark schedule. Measurement occurred during the dark portion of the cycle. One group (n=8) received BSR electrodes as described below. A second group of rats (n=8) where used for measurement of reward threshold.
Stereotaxic Surgery: The rats used in the BSR research under appropriate methods were given approved anesthesia and then surgically implanted with a single bi-polar electrode aimed at the lateral hypothalamus under IACUC approved surgical, anesthetic and post-operative procedures. Localization of the site of stimulation was verified histological post experimentation.
Apparatus: BSR stimulation was delivered using a +/_ biphasic pulses delivered by a constant current stimulator control by a computer. Animals pressed a lever on a continuous reinforcement (CRF) schedule in operant chambers with two levers (one was active) to receive reward. Performance was collected at the end of the session on lab computers.
Procedure: During the dark portion of the light-dark cycle experimental subjects were given an operant sessions in which they were shaped to lever press for stimulation. Rats were first tested one hour into this period (baseline/pre-manipulation testing with ad libitum food and water), and then after 24 h of food deprivation (water remained ad lib.). Brain stimulation parameters: biphasic square wave stimulation, delivered at 100 Hz, stimulation train was 0.2 s with each response. Current intensities varied from 10 to 100 uA (amperes) descending in intensity to determine threshold.
You will analyze the data for responding and threshold using Students t – test of mean differences in brain stimulation threshold and responding between baseline and food deprivation conditions. The appropriate t-test is a within analysis using a single sample under two conditions. The data will include all 8 of the rats in each condition. These values will be presented in two figures: Figure 1 BSR responding or response rate data, baseline vs deprivation; Figure 2 BSR threshold data baseline vs deprivation.
First in text presenting the findings in order: Refer to the figure as well as present means and statistics. Figure 1: Effects of food deprivation on BSR responding.
Refer to the figure as well as present means and statistics. Figure 2. Effects of food deprivation on threshold for BSR.
Note: At least four research articles should be cited and appear in the reference section. At least two other peer reviewed papers or other references also should be included. This is a minimum, more is better.
Discuss the results findings: Responses and threshold changes with food deprivation. The finding of food deprivation effects on BSR and other behaviors in the literature. Also discuss the relationship of reward to nutrient intake and the superiority of threshold over simple response rate, as well as more recent findings in the literature, and drug research with BSR are also appropriate here.
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