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This paper provides a critical review of several possible mechanisms at different levels of analysis underlying the effects and therapeutic potential of psychedelics. At the (1) biochemical level, psychedelics primarily affect the 5-HT 2A receptor, increase neuroplasticity, offer a critical period for social reward learning, and have anti-inflammatory properties. At the (2) neural level, psychedelics have been associated with reduced efficacy of thalamo-cortical filtering, the loosening of top-down predictive signaling and an increased sensitivity to bottom-up prediction errors, and activation of the claustro-cortical-circuit. At the (3) psychological level, psychedelics have been shown to induce altered and affective states, they affect cognition, induce belief change, exert social effects, and can result in lasting changes in behavior. We outline the potential for a unifying account of the mechanisms underlying psychedelics and contrast this with a model of pluralistic causation. Ultimately, a better understanding of the specific mechanisms underlying the effects of psychedelics could allow for a more targeted therapeutic approach. We highlight current challenges for psychedelic research and provide a research agenda to foster insight in the causal-mechanistic pathways underlying the efficacy of psychedelic research and therapy. • This paper comprehensively reviews the pharmacological, neural and psychological mechanisms underlying psychedelics. • We critically evaluate the merits and pitfalls of each explanatory mechanism. • We provide a research agenda for psychedelic research, including a theory of pluralistic causation. [ABSTRACT FROM AUTHOR]

The scientific study of human behavior from a modern evolutionary perspective began in the 20th century with disciplines such as human ethology and behavioral ecology as well as sociobiology. This early work focused on the characterization of a universal human nature that could be observed across all societies and cultures, one believed to have emerged in part from evolutionary processes. With the passage of time a newer evolutionary discipline, evolutionary psychology, emerged in the early 1990 s and quickly flourished. The focus on human nature was retained from its forerunners, but the primary focus of the field underwent a decided shift. Gone was the emphasis on observable behaviors and in its place moved psychological and cognitive functioning. At the same time, the new field took an interesting departure from other branches of psychology by largely relegating the significance of individual differences across cognitive and personality styles (whether heritable or environmental in origin) to a minor role. In this paper, we review the primary original arguments for minimizing or ignoring the importance of individual differences in personality and cognition, all in the service of making the case that the study of human nature, and evolutionary psychology more generally, is not at odds with individual differences research. The two fields have always been complementary, with one serving as a frequent source of insight for the other. [ABSTRACT FROM AUTHOR]