Spine dynamics in the brain, mental disorders and artificial neural networks

• Published in: Nature reviews. Neuroscience Vol. 22; no. 7; pp. 407 - 422
• Main Authors: Kasai, Haruo, Ziv, Noam E., Okazaki, Hitoshi, Yagishita, Sho, Toyoizumi, Taro
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2021; Nature Publishing Group
• Subjects: 631/378/1689/1761; 631/378/2597; Algorithms; Animal Genetics and Genomics; Artificial intelligence; Behavioral Sciences; Biological Techniques; Biomedical and Life Sciences; Biomedicine; Dendritic spines; Dopamine; Evaluation; Identification and classification; Learning algorithms; Machine learning; Mental disorders; Mental illness; Neural networks; Neurobiology; Neurosciences; Review Article; Spine; Structure; Synapses; Synaptic plasticity; Japan
• ISSN: 1471-003X; 1471-0048; 1471-0048; 1469-3178
• DOI: 10.1038/s41583-021-00467-3

In the brain, most synapses are formed on minute protrusions known as dendritic spines. Unlike their artificial intelligence counterparts, spines are not merely tuneable memory elements: they also embody algorithms that implement the brain’s ability to learn from experience and cope with new challenges. Importantly, they exhibit structural dynamics that depend on activity, excitatory input and inhibitory input (synaptic plasticity or ‘extrinsic’ dynamics) and dynamics independent of activity (‘intrinsic’ dynamics), both of which are subject to neuromodulatory influences and reinforcers such as dopamine. Here we succinctly review extrinsic and intrinsic dynamics, compare these with parallels in machine learning where they exist, describe the importance of intrinsic dynamics for memory management and adaptation, and speculate on how disruption of extrinsic and intrinsic dynamics may give rise to mental disorders. Throughout, we also highlight algorithmic features of spine dynamics that may be relevant to future artificial intelligence developments. Dendritic spines can be considered to embody algorithms that underlie various brain functions. Here, Kasai et al. review spine dynamics and their roles in various brain functions, compare these dynamics with parallels in machine learning and describe how disrupted dynamics may contribute to mental disorders.