Neural Circuit Motifs in Valence Processing

Abstract

How do our brains determine whether something is good or bad? How is this computational goal implemented in biological systems? Given the critical importance of valence processing for survival, the brain has evolved multiple strategies to solve this problem at different levels. The psychological concept of "emotional valence" is now beginning to find grounding in neuroscience. This review aims to bridge the gap between psychology and neuroscience on the topic of emotional valence processing. Here, I highlight a subset of studies that exemplify circuit motifs that repeatedly appear as implementational systems in valence processing. The motifs I identify as being important in valence processing include (1) Labeled Lines, (2) Divergent Paths, (3) Opposing Components, and (4) Neuromodulatory Gain. Importantly, the functionality of neural substrates in valence processing is dynamic, context-dependent, and changing across short and long timescales due to synaptic plasticity, competing mechanisms, and homeostatic need.

Keywords: BLA; Divergent Paths; Opposing Components; amygdala; circuits; emotion; lateral hypothalamus; motivation; neural; valence.

Figure 1. Defining concepts with terminology.

Schematic differentiating related, but distinct, terms in emotion research. Green represents positive valence, while red represents negative valence. Valence refers to the “sign” of the state, with positive representing rewarding states and negative representing aversive ones. Value tracks the worth of external stimuli on a continuum analogous to integers that can be positive or negative. Intensity indicates the absolute value of the strength of an internal state.

Figure 2. Key theories of emotional processing.

In both theories valence is conceptualized distinctly from arousal level. In one framework it is a subsequent step, in another it is on a distinct axis.

Figure 3. Motifs in the neural circuit mechanisms of valence processing.

Four motifs are depicted on an implementational level. Motif 1, Labelled Lines represents a circuit with parallel sensorimotor paths for positive and negative stimuli that directly relay to downstream circuits driving approach and avoidance that do not interact or influence each other, which lends the algorithmic advantage of speed and robustness. Motif 2, Divergent Paths represents a circuit that receives the same sensory input but diverges to distinct downstream targets steered by synaptic weights and offers the advantages of associative plasticity, flexibility, and reversal. Motif 3, Opposing Components represents a circuit which, within an anatomically defined projection, contains neurons of diverse functionality that can serve to coordinate, regulate, and weigh different inputs. Motif 4, Neuromodulatory Gain represents a circuit wherein concentration-dependent activation of metabatropic receptors can extend plasticity time scales to allow for single-trial learning, state-dependency, and context-switching.