Interoception

[12] Visceroception refers to the perception of bodily signals arising specifically from the viscera: the heart, lungs, stomach, and bladder, along with other internal organs in the trunk of the body.

The most commonly studied system is cardiovascular interoception which is typically measured by directing attention towards the sensation of the heartbeat during various tasks.

In Sherrington's model, exteroceptive receptors were those that received information from outward stimuli, like light, touch, sound, and odor.

For him, interoceptors (a term which has lost prevalence in modern literature) were thus confined to visceral involuntary smooth muscle (e.g. surrounding blood vessels).

[18] Further work on interoceptive processing after Sherrington was delayed for many years owing to the influential claim by John Newport Langley that the autonomic nervous system used only efferent (brain-to-body) signaling to implement its functions.

During that period, some researchers chose to use the terms visceroceptor and interoceptor interchangeably, in line with Sherrington's usage,[20] others combined proprioceptive and visceroceptive information into one category—interoception—based on physiological data about the lack of differences in nerve impulses,[22][23] and still others proposed that interoception includes more than just endogenous (internal) stimuli.

[14] In a similar vein, neuroanatomists hoping to find the anatomical basis of interoceptive functioning have stated the existence of a homeostatic pathway from the body to the brain that represents "the physiological status of all tissues in the body," and that this mapping onto the brain provides an individual with subjective feeling states that are critical for human emotion and self-awareness.

The regulatory model of allostasis claims that the brain's primary role as an organ is the predictive regulation of internal sensations.

Importantly, interoception is made possible through a process of "integrating the information coming from inside the body into the central nervous system".

[30] This definition deviates from Sherrington's original proposition, but exemplifies the dynamic and widening breadth of interoception as a concept in modern literature.

Heartbeat detection is commonly used because of its ability discern an individual's performance above chance levels, so-called "good detectors".

[39][40] This approach provides a physiological basis for understanding psychiatric and neurological disorders that are characterized by heightened sympathetic nervous system activity.

[43] Rectal and bladder distensions are used as a method to perturb the homeostatic environment of the gastrointestinal and genitourinary systems, using placement of balloon catheters which can be inflated to achieve different stimulus intensities.

Associative fear learning paradigms have been used to study how innocuous signals might lead to abnormal states of gastrointestinal hypersensitivity and anxiety.

[46] Thus while pain was once thought of as an exteroceptive sensation, based on functional imaging and anatomical evidence it is now understood that it has an interoceptive component.

These sensory and affective characteristics of thermoregulation may motivate certain behavioral responses depending on the state of the body (for example, moving away from a source of heat to a cooler space).

Such perturbations in the internal homeostatic environment of an organism are thought to be key aspects of a motivational process giving rise to emotional states, and have been proposed to be represented principally by the insular cortex as feelings.

[49] Soft touch activates the insula rather than the somatosensory cortex, indicating that it has an affective importance absent in Aβ fibers.

The ventromedial posterior nucleus (VMpo) is a subregion of the thalamus which receives sympathetic information from lamina I spinothalamic neurons.

The insula is considered to be a "hub" region because it has an extremely high number of connections with other brain areas, suggesting it may be important for an integration of lower-level physiological information and salience.

[52] The anterior insular cortex (AIC) is involved in the representation of "cognitive feelings" which arise from the moment-to-moment integration of homeostatic information from the body.

This area of the brain is commonly engaged by gastrointestinal distension and nociceptive stimulation, but it likely plays a role in representing other interoceptive sensations as well.

[58] The somatic marker hypothesis, proposed by Antonio Damasio, expands upon the James-Lange theory and posits that decisions and the ensuing behaviors are optimally guided by physiological patterns of interoceptive and emotional information.

[59][60][61] In another model, Bud Craig argues that the intertwining of interoceptive and homeostatic processes is responsible for initiating and maintaining motivational states and engendering human self-awareness.

[1] Patients with generalized anxiety disorder (GAD) frequently report being bothered by interoceptive feelings of muscle tension, headaches, fatigue, gastrointestinal complaints, and pain.

Functional neuroimaging studies have shown that posttraumatic stress disorder (PTSD) patients exhibit a decreased activation in the right anterior insula, a region of the brain that is largely responsible for identifying the mismatch between cognitive and interoceptive states.

[68] Other studies have found that interoceptive accuracy is increased in these patients, as evidenced by their superior ability in heartbeat detection tasks in comparison to healthy controls.

[84] However, it has also been found that children with ASD actually show greater interoceptive sensitivity than control subjects when measured over a long period of time.

The EPIC model[4] deviates from this and proposes that the brain is involved in a process of active inference,[85][86] that is, assiduously making predictions about situations based on previous experiences.

[95] Meditation and mindfulness have been looked into as possible techniques to enhance interoceptive awareness based on their tendency to redirect focus within oneself.