Department of Physiology, Showa University School of Medicine, Hatanodai 1-5-8, Shinagawa-ku, Tokyo 142-8555, Japan
Respiration is primarily regulated for metabolic and homeostatic purposes in the brainstem. However, breathing can also change in response to changes in emotions, such as sadness, happiness, anxiety or fear. Final respiratory output is influenced by a complex interaction between the brainstem and higher centres, including the limbic system and cortical structures. Respiration is important in maintaining physiological homeostasis and co-exists with emotions. In this review, we focus on the relationship between respiration and emotions by discussing previous animal and human studies, including studies of olfactory function in relation to respiration and the piriform–amygdala in relation to respiration. In particular, we discuss oscillations of piriform–amygdala complex activity and respiratory rhythm.
Respiratory chest wall movement is performed by the intermittent contraction of inspiratory and expiratory respiratory muscles. Motor commands for the contraction of these muscles are generated in complex neuronal networks in the brain. Various afferent inputs are integrated to produce respiratory rhythm and tidal activity, primarily in response to metabolic demands. The most important inputs for the regulation of breathing involve chemoreceptors that form reflex feedback mechanisms for respiratory motor activities. However, respiratory motor output is also influenced by internal and external environmental changes. This is called behavioural breathing and is generally considered to have a different mechanism from metabolic breathing.
Final motor outputs for breathing are generated by motoneurons in the spinal cord. Descending autonomic (metabolic) and voluntary breathing pathways to spinal motoneurons from higher centres are essentially and functionaly different. The origin of the voluntary control of breathing is in the cerebral cortex; stimulation of the primary motor cortex induces contraction of the diaphragm and intercostal muscles in humans (Gandevia & Rothwell, 1987; Gandevia & Plassman, 1988). This primary motor area has been shown by transcranial magnetic stimulation to coincide with the middle cortex 1 cm posterior to the vertex (Maskill et al. 1991). Aminoff & Sears (1971) reported in cats that electrical stimulation of the cerebral cortex at the vertex induces short-latency activation of contralateral motoneurons of the intercostal muscles. Transection of the dorsolateral columns of the spinal cord abolishes responses to electrical stimulation. However, transection does not affect the spontaneous rhythmic activities of the intercostal muscles.
The medulla oblongata and pons comprise the centre for metabolic breathing; this pathway descends along the spinal ventrolateral column as the bulbospinal pathway. The descending tract for autonomic inspiration is located laterally in the ventrolateral column, whereas the tract for expiration is located ventrally. Transection of the tract abolishes autonomic rhythmic breathing but has no effect on responses of the respiratory muscles to cortical stimulation.
Beside these studies that show the different pathways for metabolic and behavioural breathing, studies of Orem and Trotter show the cortical projections to brainstem respiratory neurons (Orem, 1989; Orem & Trotter, 1994), indicating that behavioural influences arising from higher centres modify metabolic breathing patterns.
Autonomic breathing is not only controlled by metabolic demands but also constantly responds to changes in emotions, such as sadness, happiness, anxiety and fear. Final respiratory output involves a complex interaction between the brainstem and higher centres, including the limbic system and cortical structures. It is interesting that respiration, which is important in maintaining physiological homeostasis, and emotions co-exist. In this review, we focus on the relationship between respiration and emotions by discussing previous studies of olfactory function and respiration.
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