Dr. Valeri Farmer-Dougan
Dr. Valeri A. Farmer Dougan
Office – 413 DEG, Lab - 230 FSA
Phone – 309-438-7420 Email - vfdouga@ilstu.edu
The behavioral neuroscience laboratory (Felmley 230) focuses on behavioral and neural mechanisms mediating reward optimization in both individual and groups of animals. I am particularly interested in the role of dopamine as a behavioral activator during foraging and matching paradigms. Understanding how organisms optimize reward is important not only for understanding animal behavior, but for understanding human neuropathologies such as addiction, schizophrenia or attention disorder.
Changes in sensitivity to reward using a Matching Law Paradigm
The matching law, an optimization model, can be used to measure an animal’s sensitivity to reward. This paradigm may be used to examine the role of DA in choice behavior. DA, considered the neural substrate of reward, appears instead to modulate arousal, which in turn affects sensitivity to reward. Our lab has found that DA, D1 and D2 agonists differentially disrupt sensitivity to reward, suggesting differences in DA receptor functions. The focuses of these projects, then, are the parameters that impact reward sensitivity.
Effects of Ephedrine, Caffeine, and Their Combination on the Reinforcement Sensitivity of the Rats
Ephedrine, a central nervous and cardiovascular systems stimulant, has been increasingly abused for weight loss, sexual stamina, and increased behavioral activation. Evidence suggests that caffeine can also increase an organism’s behavior activation levels. Recent research has implied that an ephedrine and caffeine combination improves vigilance and attention at low doses (possibly increasing sensitivity to reinforcement), but may also produce psychosis, which is detrimental to sensitivity to reinforcement. However, no recent investigations tested changes in sensitivity to reward using these drugs individually or in combination. The proposed study will examine changes in sensitivity to reinforcement across a series of concurrent variable interval schedules when rats are treated with ephedrine, caffeine, or a combination. It is expected that changes in animal’s sensitivity to reward would both dose and drug dependent. Specifically, it is predicted that doses of caffeine or ephedrine alone will improve the animal’s sensitivity to reinforcement, while combinations of the drugs should decrease it.
Effects of Competition on Matching in an Open Foraging Paradigm
The matching law and ideal free distribution theories predict that the ratio of time spent at two patches will equal the ratio of food resources obtained at the two patches. Many studies using an open field foraging paradigm have shown overall group matching. Interestingly, individual members of the group do not necessarily match. Rather, some match, others overmatch and still others undermatch, suggesting competition affects individual matching. Few investigations, however, have directly assessed the role of competition on matching. One approach may be to compare matching when the animal forages alone and then with a competitor. It can be predicted that pairing an animal with a higher status competitor will result in undermatching. The animal should show more frequent and/or longer visits to the poorer patch. Alternatively, if the animal is paired with a lower status individual, matching should remain either unchanged or produce overmatching. The present experiment examined matching in pairs of rats foraging at two patches for food resources. Animals were initially exposed to solitary foraging conditions, and then were introduced to a competitor. Data suggest that individual rats matched, and that competition disrupted the initial matching values. The effects of competition on matching are then discussed.
Behavioral Contrast in Group Foraging
Multiple schedule behavioral contrast is an inverse relationship between the rate of responding in one component of a multiple schedule and the conditions of reinforcement in the other component (McSweeney and Weatherly, 1998). Positive contrast is said to occur when an increase in responding during occurs in the constant (contrast) component when the conditions of the other (variable) component worsen. This has been well demonstrated with individual animals using a variety of reinforcement situations and across several response manipulanda. It has not, however, been studied with groups of animals in a foraging setting. In the present experiment, five rats were placed in a large open foraging box in which two feeders at opposite ends released food pellets according to a multiple VI VI schedule. The rats were exposed to three baseline sessions (MULT VI 15 VI 15), 5 sessions of a contrast condition (MULT VI 15 VI 900), and then returned to the baseline condition for three additional sessions. Data suggested a strong group behavioral contrast effect.
Effects of Ephedra and Haliperidol on Multiple Schedule Behavioral Contrast: Attenuating or Intensifying Habituation Effects
Multiple schedule behavioral contrast is an inverse relationship between the rate of responding in one component of a multiple schedule and the conditions of reinforcement in the other component (McSweeney and Weatherly, 1998). Positive contrast is said to occur when an increase in responding during occurs in the constant (contrast) component when the conditions of the other (variable) component worsen. While several theories exist to explain the phenomenon, one model that of habituation, is currently the dominant model. This theory states that within session changes in operant responses occur because subjects sensitize and then habituate to the reinforcer. If this is true, than drugs which alter the arousal state of the animal should increase or decrease sensitization to the reinforcer, and thus either attenuate or intensify the contrast effect. This is the focus of the present set of experiments. We will attempt to manipulate arousal using a general dopamine agonist, ephedra, and a dopamine d2-antagonist, haloperidol. It is expected that haloperidol should intensify while ephedra should attenuate the behavior contrast.
Optimal Foraging, Competition and Dopamine
Matching in individual animals, and foraging in groups of animals is established. However, little data exist examining the role of the individual in group foraging. DA may also play a role in group foraging. For example, changes in DA levels have been found between solitary and group-reared animals, and rats presented with a more dominant rat have show decreased DA levels. Thus, my lab is conducting a series of studies examining the role of individual animal behavior on group foraging, and how changes in DA may alter group matching.
Development of a Predictive Neural Deficit Behavior Inventory
My lab has recently developed an novel avoidance task using fox urine paired with a predictive stimulus. Behavioral changes in avoidance pre- to post-stroke are then paired with Magnetic Resonance Imaging (MRI) and histological analyses. Our hope is to develop a behavior inventory predictive of neural injury that may be given within 6 to 8 hours of the neural insult. Predictive assessment of neural damage could potentially direct the type and improve and guide the use of interventions for animals, and eventually humans who have suffered a cerebral infarct.