Defined as the sense of the internal state of the body.
This can be both conscious and non-conscious process.
It involves integrating signals of the brain relayed from the body into specific subregions: brainstem, thalamus, insula, somatosensory, and anterior cingulate cortex.
Interoception is the ability to sense and perceive signals from within the body, such as hunger, thirst, pain, and muscle fatigue.
It involves a complex network of neural pathways that communicate between the body and the brain.
The accuracy of interceptive signals is important for maintaining physiological homeostasis, particularly in regards to regulating autonomic and emotional responses.
There is also growing evidence that interceptive awareness can influence overall well-being and mental health.
This allows for a representation of the physiological state of the body.
Interoception maintains homeostatic conditions in the body and, potentially, facilitating self-awareness.
It is involved in many different physiological systems: cardiorespiratory system, gastrointestinal system, nociceptive system, endocrine and immune systems.
Interoceptive signals enter the brain via a neural pathways that allow for the sensory processing and prediction of internal bodily states.
When misrepresentations of internal states, or a disconnect between the body’s signals and the brain’s interpretation and prediction of those signals, may underlie some mental disorders such as anxiety, depression, panic disorder, anorexia nervosa, bulimia nervosa, posttraumatic stress disorder (PTSD), obsessive compulsive disorder (OCD), Attention deficit hyperactivity disorder (ADHD), autism spectrum disorders, somatic symptom disorder, and illness anxiety disorder.
The term 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 term visceroception does not include organs like the brain and skin, while interoception encompasses visceral signaling, it more broadly relates to all physiological tissues that relay a signal to the central nervous system about the current state of the body.
Interoceptive signals are transmitted to the brain via multiple pathways: the lamina I spinothalamic pathway, the viscerosensory pathway, the vagus and glossopharyngeal nerves, chemosensory pathways in the blood, and somatosensory pathways from the skin.
Interoceptive signals come from many different physiological systems.
The interoceptive systems include: cardiovascular interoceptive , respiratory system, gastrointestinal and genitourinary systems, nociceptive system, thermoregulatory system, endocrine, immune systems, and soft cutaneous touch.
Interoceptive sensations may be important for learned behavior and emotion.
It is proposed that the brain’s primary role as an organ is the predictive regulation of internal sensations.
Predictive regulation is indicative ofthe brain’s ability to anticipate needs and prepare to fulfill them before they arise:
the brain is responsible for efficient regulation of its internal milieu.
Interoception is a process of integrating information from inside the body into the central nervous system.
The detection reflects the presence or absence of a conscious report of interoceptive stimuli, like a heartbeat or growling stomach.
The magnitude of stimuli is the intensity of the stimulus, or how strongly the stimuli is felt.
Interoceptive discrimination describes the ability to localize interoceptive stimuli in the body to specific organs and differentiate them from other bodily stimuli that also occur, like distinguishing between a heart which is beating hard from an upset stomach.
Respiratory perception differs from other interoceptive symptoms because of the ability to exert voluntary control over the system with controlled breathing or breathing exercises.
Interoceptive sensations related to the gastrointestinal and genitourinary systems are hunger and fullness.
The dorsal mid-insula aspect of the brain is integral in taste processing during gastrointestinal interoceptive attention tasks.
Innocuous signals might lead to abnormal states of gastrointestinal hypersensitivity and anxiety.
Nociception refers to the receiving and processing of pain inducing stimuli by the central nervous system.
Functional brain imaging studies during painful stimulation of the skin suggests that the insular cortex is prominently activated during pain processing.
Pain has an interoceptive component.
Temperature and pain are represented as feelings of coolness/warmness and pleasantness/unpleasantness in the brain.
These sensory characteristics of thermoregulation may motivate behavioral responses depending on the state of the body: moving away from a source of cold to a warmer space
Perturbations in the internal homeostatic environment are key aspects of a motivational process giving rise to emotional states, and are proposed to be represented by the insular cortex as feelings.
It is known that the endocrine and immune systems are necessary body systems that aid in homeostatic control.
When imbalances occur in these systems, they may lead to to interoceptive dysregulation in depression, and lead to hyperawareness of interoceptive signaling and a hypo-awareness of exteroceptive signaling.
Soft touch refers to the stimulation of slow, unmyelinated C tactile afferent nerve fibers.
Soft touch is associated by a sense of pleasantness, and is likened to other interoceptive modalities: thermoregulation and nociception because of the similarities in anatomical function.
Soft touch activates the insula rather than the somatosensory cortex, indicating that it has an affective importance.
Soft touch utilizes a separate pathway, and it may have a social relevancy: allows the body to separate
outward stimuli from stimuli that evokes an affective feeling.
Neural pathways relay information to allow interoceptive processing from the body to the brain: the spinothalamic pathway, the visceroceptive pathway, and the somatosensory pathway.
The spinothalamic pathway carries information to the brain about temperature and pain, but it may relay all information about the homeostatic condition of the body.
The spinothalamic pathway afferent signals enter through the spinal cord at the superficial layer of the dorsal horn:
Second order neurons cross the midline of the spinal cord and project up the opposite side, synapsing on the nucleus of the solitary tract, parabrachial nucleus, and periaqueductal gray in the brainstem.
Third order neurons in the ventromedial posterior nucleus in the thalamus relay the signal to the dorsal posterior insula.
The visceroceptive pathway relays information about visceral organs to the brain.
Afferent signals from the vagus nerve enter the brainstem making synaptic connections with the nucleus of the solitary tract and parabrachial nucleus.
The signal is relayed to the ventromedial basal nucleus of the thalamus.
Third order neurons send the signal to the posterior insula.
The somatosensory pathway relays information about proprioception and discriminative touch to the brain through different receptors in the skin.
Afferent signals from the mechanoreceptors or proprioceptors enter the spinal cord at the dorsal root ganglia
Second order neurons cross the midline in the medulla, projecting up the opposite side and synapse on third order neurons in the ventral posterior lateral nucleus or ventromedial posterior nucleus of the thalamus.
Third order neurons in the thalamus relay the signal to the primary somatosensory cortex in the brain.
The thalamus receives signals from sympathetic and parasympathetic afferents during interoceptive processing.
The ventromedial posterior nucleus subregion of the thalamus which receives sympathetic information from lamina I spinothalamic neurons and is important for processing of nociceptive, thermoregulatory, and visceral sensations.
The ventromedial basal nucleus (VMb) receives parasympathetic information from visceral and gustatory systems.
The ((insula)) is critically involved in the processing, integration, and cortical representation of visceral and interoceptive information.
Lamina I spinothalamic and vagal afferents project to the brainstem and thalamus to the posterior and mid dorsal insula respectively.
Information travels to the posterior and mid-insula, which combines visceral and somatosensory information.
The insula is also activated during a variety of exteroceptive and affective tasks.
The insula is a hub region because its an high number of connections with other brain areas, suggesting it may be important for an integration of lower-level physiological information and salience.
The insula connects to many regions in the brain and is highly involved in many homeostatic functions.
The anterior insular cortex (AIC) represents cognitive feelings which arise from the moment-to-moment integration of homeostatic information from the body.
Such cognitive feelings engender self-awareness by creating a sentient being aware of bodily and cognitive processing.
The insular cortex differs cytoarchitecturally on its anterior, mid, and posterior regions.
The posterior insular cortex is granular in nature.
The mid insular cortex is slightly granulated.
The anterior insular cortex has no granulation.
The three portions of the insular cortex are important for different levels of functional connectivity.
Information from the thalamus is projected to all three regions of the insula.
Areas of the insula with increased granulation are considered to be capable of receiving sensory input.
The anterior cingulate cortex (ACC) plays a significant role in motivation and the creation of emotion.
Feeling is represented in the insula, while the motivationis represented in the anterior cingulate cortex.
Many interoceptive tasks activate the insula and ACC together: specifically tasks that elicit strong aversive feeling states like pain.
The sensory motor cortex provides an alternative pathway for sensing interoceptive stimuli.
Skin afferents which project to the primary and secondary somatosensory cortices provide the brain with information regarding bodily information.
The relationship between interoception and emotional experience is an intimate one.
Ones physiological body states are the critical ingredients for emotional experience and consciousness.
The intertwining of interoceptive and homeostatic processes is responsible for initiating and maintaining motivational states and engendering human self-awareness.
Interoception and mental health
Disturbances of interoception occur frequently in psychiatric disorders.
Panic disorder patients report a heightened experience of interoceptive sensations.
Panic disorder patients feel heartbeat sensations more intensely when the state of the body is perturbed by pharmacological agents, suggesting heightened sensitivity to experiencing interoceptive sensations.
With generalized anxiety disorder (GAD) patients frequently report being bothered by interoceptive feelings of muscle tension, headaches, fatigue, gastrointestinal complaints, and pain.
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.
It is suggested that PTSD patients experience reduced interoceptive awareness.
Patients with anxiety disorders experience heightened awareness of and accuracy in identifying interoceptive processes: suggested by hyperactivation in the anterior cingulate cortex, a region of the brain associated with interoception in several different kinds of anxiety disorders.
Interoceptive accuracy is increased in patients with anxiety disorders as evidenced by their superior ability in heartbeat detection tasks in comparison to healthy controls.
Anorexia nervosa is associated with interoceptive disturbances.
Patients with anorexia nervosa often develop insensitivity to interoceptive cues of hunger.
Patients with anorexia nervosa often are highly anxious and report disturbed interoceptive experiences, concentrate on distorted perceptions of their body in fear of weight gain, they also report altered physical states within their bodies, such as indistinct feelings of fullness, or an inability to distinguish emotional states from bodily sensations.
The inability to distinguish emotional states from bodily sensations in general is called ((alexithymia)).
Patients with bulimia nervosa (BN) exhibit abnormal interoceptive sensory processing, and reduced interoceptive awareness.
Bulimia nervosa (BN) patients have reduced sensitivity to various internal and external sensations, and exhibit an increased threshold to heat pain, compared to others.
Bulimia nervosa (BN) patients have increased gastric capacity.
Neuroimaging in BN patients have an increased activity and volume in the insula and anterior cingulate cortex.
When looking at food BN patients have increased activity in regions associated with interoception and taste processing.
It is suggested that major depressive disorder (MDD) is linked to interoceptive dysfunction.
Women with MDD are less accurate on heartbeat counting tasks than are men with MDD.
Patients with MDD are less accurate at counting heartbeat than are patients with panic or anxiety disorders.
Depressed patients experiencing high levels of anxiety are more accurate on heartbeat detection tasks than depressed patients with lower levels of anxiety.
Patients with somatic symptom disorders score lower on heartbeat detection tasks than healthy controls: nteroceptive accuracy is poor in psychosomatic disorders.
Patients with psychosomatic disorders who are anxious or stressed report physical symptom discomfort at lower heart rates during exercise treadmill tests.
Patients with psychosomatic disorders appear to have poorer interoceptive distress tolerance in somatic symptom disorders with comorbid psychiatric conditions.
Patients with obsessive compulsive disorders (OCD) are more accurate on a heartbeat perception task than healthy controls and anxiety in such patients heightens interoceptive awareness.
Patients with autism spectrum disorder (ASD) have poorer interoceptive awareness than others.
There appears to be a link between interoceptive processing and mental disorders.