Since time immemorial, animals have sought rewarding stimuli because they result in pleasant sensations. In the animal kingdom, the search for rewards, such as water, food and sex, among others, is closely linked to the survival of an individual and the species as a whole. The stimuli that lead to such actions are intrinsic or unconditioned (US) stimuli. These stimuli lead to a natural pleasant response, also known as the unconditioned response (UR). These stimuli are intrinsically present, while others must first be learned to result in a reward. We call these extrinsic or conditioned stimuli (CS), such as work that must be rewarded with money (conditioned response or CR). For an organism to establish this connection, a CS normally coexists with a US during a training phase. Scientifically speaking, the search for reward induces specific behaviors in an organism. We can thus discern different reward-seeking functions. Dopamine has long been involved in motivation, learning and reward seeking. These behavioral processes are intimately linked to each other and different areas of the brain have been shown to play essential roles in these processes. To further add to the complexity and confusion of the system, other pathways overlap with the dopaminergic system, such as the serotonergic, cholinergic, GABAergic, orexinergic, and noradrenergic systems. Say no to plagiarism. Get a tailor-made essay on “Why violent video games should not be banned”? Get an original essay The interaction of anatomically distinct brain areas in the dopamine system gives rise to different types of learning and motivation stages. Ventral tegmental area and reward prediction error The ventral tegmental area (VTA) is a key area of ​​the mesocorticolimbic dopaminergic system. The VTA receives information from sensory systems and its dopamine neurons project to several other brain structures involved in motivation and learning, such as the core and shell of the nucleus accumbens and the prefrontal cortex. The VTA shows strong dopaminergic activity during reward-related learning in the form of phasic DA pulses. In the pioneering study by Schulz et al. (1997), it was shown that there was a significant increase in dopamine levels in the VTA of the monkey brain when performing a learning task upon initial consumption of a reward. After the training phase, phasic dopaminergic impulses were already observed during the presentation of the first environmental cue (appearance of a light indicating to press the lever to obtain a reward), but the initial phasic dopaminergic impulses decreased during consumption of the reward. On the other hand, inactivation of dopamine signaling in the VTA and NAc (inactivation of D2 receptors) has generally been shown to underlie aversive learning. These phasic dopaminergic impulses are strongly correlated with reward-seeking behavior and learning. This pulsing of the DA neuron is generally said to encode what is called a “reward prediction error” (RPE). RPE is the actual value of a rewarding stimulus minus the expected value of a rewarding stimulus. Therefore, RPE can be distinguished into positive RPE, neutral RPE or negative RPE. A positive RPE indicates that the final reward was more pleasant than initially expected, which leadsgenerally to learning, so that the environmental signals leading to this reward are identified. A positive RPE can also come from a surprising positive reward. A neutral RPE indicates that the expected pleasant sensation of a reward was the same as the actual outcome. In a negative RPE, the reward was, so to speak, disappointing, that is, the result was less satisfactory. A negative RPE induces aversive learning in order to avoid future unpleasant or painful situations. Dorsal dopamine neurons in the VTA typically show decreased activation to noxious stimuli (footshock), while increased activity can be seen in ventral dopamine neurons in the VTA. A hindpaw foot shock of anesthetized rats was applied and the activity of DA neurons in the dorsal and ventral VTA was recorded. In the upper figure, we see an initial decrease in DA neuron firing in the dorsal VTA. A noxious stimulus inhibits this neuronal activity. In the bottom figure, there is a large initial increase in DA neuron firing in the dorsal VTA. These neurons are excited by a noxious stimulus. Dopamine is not the only neurotransmitter acting in the mesolimbic pathway. The mesolimbic dopamine pathway has been shown to be subject to cholinergic modulation and transient vanilloid 3 receptor potential in the VTA.Dopamine in the nucleus accumbens core and shellThe nucleus accumbens (NAc) is part of the mesolimbic pathway and receives inputs from the VTA. It is important to understand that the NAc core and NAc shell calculate neural inputs for different types of learning. The NAc core also performs RPE computation while the NAc shell is involved in incentive salience. This can be a source of confusion, as it appears that NAc shell activity generally shows high activity in terms of incentive salience, while the NAc core is best studied with reward-related theories, although it is also active in terms of incentive salience. Nucleus accumbens core measurements are represented by the bold black line, Nucleus accumbens shell measurements are represented by the bold gray line. DA neuron signaling was measured in the core and shell of the nucleus accumbens in mice during a lever pressing task. Maximum values ​​are reached by pressing the first lever (SLp) in the core and shell. As the mouse completes the task, dopamine levels in the nucleus drop rapidly to baseline levels (with a smaller increase upon pressing the second lever (TL0)), while dopamine signaling Dopamine in the shell remains consistently elevated, illustrating its incentive relevance. salience. At the end of the task, dopamine signaling returned to baseline. Dopamine in the learning and extinction of fear The amygdala is an essential element in the learning of fear and necessary for the consolidation of memories associated with fear. It is also part of the mesolimbic pathway, since the VTA projects to the amygdala. Proper memory establishment also involves other brain structures such as the hippocampus and the NAc. Fear conditioning is a very rapid process in which a CS is associated with a shock US. For example, a noise (CS) occurs at the same time as a foot shock (US). Mice will show an aversive response to foot shock, but initially the sound will not induce remarkable behavior in a mouse. After the training phase, the mouse will have made a link between the sound and the foot shock (the sound predicts the foot shock), which.