| Movies of Behaving Rats (best viewed in browser with quicktime browser plug-in - instructions) Rat learning simple 2-odor discrimination problem. The rat is in a training chamber. He has been trained to sample odors from a port in the wall and respond for fluid at a well below. On each trial, the rat samples an odor. One odor means he will get sucrose at the well; the other odor predicts quinine. The rat likes sucrose but wants to avoid quinine, so he must learn to use the predictive odor cues to guide his decision to respond at the well. At the beginning of this video, the rat does not know which odor means sucrose and which odor means quinine; by the end of the video the rat has learned the odor-outcome associations and is using them to guide his decisions. By inserting bundles of very small wires into the brain, we can record electrical signals - action potentials - that neurons use to communicate with each other. This video shows the action potentials from 2 neurons on an oscilloscope. We can record action potentials in real-time in anesthetized rats and also in awake, behaving rats (like the rat in the video above). By recording action potentials in awake, behaving rats, we can decode the signal to ask what sort of information neurons in different brain regions are processing - like listening to one end of a phone conversation. By looking at multiple brain regions in a circuit, we can begin to understand how the circuit is transforming that information - like listening to both ends of a phone conversation.
Here are recording action potentials from an awake, behaving rat in real-time. This rat is performing a simple 2-odor discrimination task (described above). In this case, the rat has learned the odor problem already, and we are recording action potentials from neurons in orbitofrontal cortex as he performs the task, using the microelectrode array attached to the top of the rat's head. Each action potential is audible as a tone in the video. The video shows performance on a positive trial and a negative trial. Note that one of the OFC neurons is active during sampling of the positive odor cue and again in the well when sucrose is delivered. This "neural correlate" suggests that the neuron is processing information about the odor cue and/or the association between that odor cue and the sucrose reward. We also use classical conditioning paradigms in the lab. Classical conditioning is a type of learned behavior in which cues predict outcomes which are not contingent upon the rats behavior. This kind of task has the advantatage of allowing us to study the fundamental basis of behavior in a very simple setting. In this video, a rat has learned that a light conditioned stimulus (CS) is paired with delivery of a food unconditioned stimulus (US). The rat shows that it has learned this association by making a conditioned response (CR) at the food cup in the wall of the chamber. Note that the rat makes this CR as soon as he sees the light CS, even though the food is never delivered until the light is turned off. This video shows locomotor behavior in 4 rats. The rats in Boxes 1 and 3 have received 14 days of exposure to cocaine; the rats in Boxes 2 and 4 are controls. The cocaine-treated rats are highly active and engage in abnormal repetitive, stereotyped movements that are not evident in the controls. This "psychomotor sensitization" is the result of changes in brain structure and function in these rats that are not present in the brains of the controls. These brain changes occur within the same brain systems that we study and are likely related to the neurobiological basis for addiction. We use measures of the disordered movement as an index of these brain changes in addiction studies.
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