an odorant, salt, or low pH) or a mechanical stimulus in the presence or the absence of food, to form positive or negative associations, respectively ( Adachi et al., 2010 Amano and Maruyama, 2011 Kauffman et al., 2010 Oda et al., 2011 Rankin, 2000 Torayama et al., 2007 Wen et al., 1997).
To form associative memories, worms are typically conditioned with a chemical (e.g. elegans can form both associative and non-associative memories ( Ardiel and Rankin, 2010 Loy et al., 2021 Sasakura and Mori, 2013). Though equipped with a small neural network, C. Moreover, the number and the identity of the neurons are invariant and individual neurons can be identified based on their position and anatomy across different individuals. Their compact nervous system consists of 302 neurons, and a detailed blueprint of all the chemical and electrical connections is available ( Cook et al., 2019 White et al., 1986 Witvliet et al., 2021). To this end, Caenorhabditis elegans worms offer an appealing research system. olfactory, gustatory, auditory, and visual), and is thought to confer improved detection and enhanced attention towards important cues encountered in the past ( Åhs et al., 2013 McGann, 2015).Įxtracting the principles by which memories are formed within neural networks requires first to identify the brain regions, and preferably, the individual coding neurons. Their learning-induced neuroplasticity was observed across various sensory modalities ( e.g. In that respect, sensory neurons also proved to play important roles in the formation of associative memories. For example, associative fear memories are thought to be distributed among the amygdala that encodes the valence, the hippocampus, which encodes the context, and the cortical neurons, which provide the specific sensory information ( Josselyn and Tonegawa, 2020). Mammalian brains are thought to encode associative memories in a decentralized fashion where interconnected areas, distributed across various areas of the brain, link up to encode memory traces.
Memory note 4 code#
In flies, olfactory associative learning is centralized in the mushroom body, where it is distributed among various neurons and synapses to code both the US valence and the CS odorant ( Bilz et al., 2020 Roselli et al., 2021 Widmann et al., 2018). Whether the CS was associated with a positive or negative experience, this valence remains associated with the CS.Īnimals have come up with different strategies for encoding associative memories. Moreover, their encoding needs to be logically integrated such that the behavioral response will match the expected valence that the CS predicts ( Josselyn and Tonegawa, 2020). To synthesize an adaptive associative memory that elicits an adaptive response upon future encounters with the CS, both the CS and the US must be encoded in the neural system. Consequently, the mere auditory cue prompted the dogs to salivate in expectation of their meal ( Pavlov, 1910). The famous pavlovian dogs set a classical example: These dogs were trained to associate a sound stimulus (the conditioned stimulus, CS) with food (unconditioned stimulus, US). An intriguing form of these behavioral adaptations is known as associative learning, where a link between two unrelated cues is formed. Learning and memory processes are presumably universal in the animal kingdom, forming the basis for adaptive behavior. This comprehensive study reveals basic memory-coding principles and highlights the central roles of sensory neurons in memory formation. The widely distributed memory suggests that integrated network plasticity, rather than changes to individual neurons, underlies the fine behavioral plasticity. Interneurons integrated the modulated sensory inputs and a simple linear combination model identified the experience-specific modulated communication routes. Moreover, when considering the collective activity of the sensory neurons, the specific training experiences could be decoded.
Interestingly, sensory neurons were primarily involved in coding short-term, but not long-term, memories, and individual sensory neurons could be assigned to coding either the conditioned stimulus or the experience valence (or both). Here, we have systematically studied how four types of associative memories (short- and long-term memories, each as positive and negative associations) are encoded within the compact neural network of Caenorhabditis elegans worms. A major goal in neuroscience is to elucidate the principles by which memories are stored in a neural network.
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