A neuromodulatory model for determining the effect of emotion-respiration-cognition coupling on the time-to-respond
Respiration and emotional stimuli modulate cognitive ability and the reaction time to generate bodily movement. To understand mechanisms for emotion-respiration-cognition coupling, first, we considered a schematic feed-forward neural network, in which neurons was biased by respiratory-relevant sensory input and the activation function of a neuron was modulated by a neuromodulator, such as norepinephrine (NE). Furthermore, we assumed that the neural model received a stimulus input and generated a response action upon the activity of the output neuron exceeding a certain threshold. Time-to-respond (TTR) was equivalently modulated by the intensity of the input bias and the neuromodulator strength for small action execution threshold; however, it was dominantly modulated by only the neuromodulator for high threshold. Second, we implemented a comprehensive model comprising a cardio-respiration relevant neuromechanical-gas system, a respiratory central pattern generator (CPG), NE dynamics to modulate neurocognitive dynamics, and a locus coeruleus (LC) circuit, which was the primary nucleus for controlling NE. The LC neurons received pCO2 or synaptic current from an inspiratory neurons, which resulted in shortened TTR by a stimulus input during inhalation. By contrast, upon receiving pulmonary stretch information, the TTR was shortened by a stimulus input during exhalation. In humans, TTR is shortened when a fear-related stimulus is presented during inhalation, and likewise, TTR is weakly-shortened when surprise-related stimulus is presented during exhalation. Hence, we conclude that emotional stimuli in humans may switch the gating strategies of information and the inflow to LC to change the attention or behavior strategy.