![]() ![]() ![]() If 5-HT is really involved in predicting aversive outcomes, then depleting it should surely have positive rather than negative affective consequences. These findings are hard to connect: the second fact seems orthogonal to the first and third, which are themselves in apparent contradiction. Furthermore, while SSRIs are used in the treatment of depression, genetically induced, constitutive decreases in the efficiency of 5-HT reuptake are a risk factor for depression. The third finding is the collection of psychopharmacological data implicating 5-HT in animal models of depression and anxiety, together with the fact that depleting 5-HT (by dietary depletion of its precursor, tryptophan) in human subjects who have recovered from depression, can reinstate an acute, at times fulminant, re-experience of subjective symptoms of the disease, as assessed by various rating scales. Second, 5-HT is involved in behavioral inhibition, preventing or curtailing ongoing actions in light of predictions of aversive outcomes. First, 5-HT is involved in the prediction of aversive events, possibly as a form of opponent to dopamine. However, despite the importance of serotonergic pharmacotherapies, notably selective serotonin reuptake inhibitors (SSRIs), the roles that serotonin plays in normal and abnormal function are still mysterious. Serotonin (5-hydroxytryptamine ) is a neuromodulator that appears to play a critical role in a wealth of psychiatric conditions, including depression, anxiety, panic, and obsessive compulsions. We suggest an interpretation of this finding that helps dissolve the apparent contradiction between the fact that inhibition of serotonin reuptake is the first-line treatment of depression, although serotonin itself is most strongly linked with aversive rather than appetitive outcomes and predictions. We show how a drop in behavioral inhibition, putatively resulting from an experimentally or psychiatrically influenced drop in serotonin, could result in unexpectedly large negative prediction errors and a significant aversive shift in reinforcement statistics. In the context of a highly simplified model of chains of affectively charged thoughts, we interpret the combined effects of serotonin in terms of pruning a tree of possible decisions, (i.e., eliminating those choices that have low or negative expected outcomes). There is considerable evidence for the involvement of serotonin in both the learning of these predictions and the inhibitory consequences that ensue, although less for a causal relationship between the two. Pavlovian predictions of future aversive outcomes lead to behavioral inhibition, suppression, and withdrawal. In (C), larger γ are advantageous, in (F), smaller γ are better. (C,F) Effect of preferentially choosing actions according to their valence on the average value of states. (B,E) Probabilities of ending thought sequence in O℘ + or O℘ −. In (D), the dash-dotted line indicates that statesįor k = (1,2,3} now have true negative values, andįor k = (1,2,3} have true positive values. ![]() There is a positive bias in all states, but it is more pronounced in the states with true negative values. ![]() The grey point display the estimated values of the states under inhibition α 5HT = 20. The reward of the states I℘ is zero and shown by the dash-dotted line. It is constant for each level and valence, or illustration, as all outcomes were assigned the same positive value (+1 or −1). (A,D) True values without inhibition are shown by the black line. Figure S2: Inhibition in a Deep Environment The outcomes O℘ are approached by sequentially walking through K = 4 levels. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |