The insulae are believed to be involved in consciousness and play a role in diverse functions usually linked to emotion or the regulation of the body's homeostasis.
One study on rhesus monkeys revealed widespread reciprocal connections between the insular cortex and almost all subnuclei of the amygdaloid complex.
It has also been shown that this region receives inputs from the ventromedial nucleus (posterior part) of the thalamus that are highly specialized to convey homeostatic information such as pain, temperature, itch, local oxygen status, and sensual touch.
[12][13] Research in rhesus monkeys has also reported that apart from numerous taste-sensitive neurons, the insular cortex also responds to non-taste properties of oral stimuli related to the texture (viscosity, grittiness) or temperature of food.
[15] Functional imaging studies on the cerebral correlates of language production also suggest that the anterior insula forms part of the brain network of speech motor control.
[17] Lesion of the pre-central gyrus of the insula can also cause “pure speech apraxia” (i.e. the inability to speak with no apparent aphasic or orofacial motor impairments).
[18] This demonstrates that the insular cortex forms part of a critical circuit for the coordination of complex articulatory movements prior to and during the execution of the motor speech plans.
[18] Importantly, this specific cortical circuit is different from those that relate to the cognitive aspects of language production (e.g., Broca’s area on the inferior frontal gyrus).
It has been speculated that these neurons are involved in cognitive-emotional processes that are specific to primates including great apes, such as empathy and metacognitive emotional feelings.
[20][21] The right anterior insula is engaged in interoceptive awareness of homeostatic emotions such as thirst, pain and fatigue,[22] and the ability to time one's own heartbeat.
Moreover, greater right anterior insular gray matter volume correlates with increased accuracy in this subjective sense of the inner body, and with negative emotional experience.
[23] It is also involved in the control of blood pressure,[24] in particular during and after exercise,[24] and its activity varies with the amount of effort a person believes he/she is exerting.
[37] One brain imaging study suggests that the unpleasantness of subjectively perceived dyspnea is processed in the right human anterior insula and amygdala.
[49][50] It has been identified as a "central command” centre that ensures that heart rate and blood pressure increase at the onset of exercise.
[54] It plays a role in a variety of homeostatic functions related to basic survival needs, such as taste, visceral sensation, and autonomic control.
The results of the social decision task yielded that individuals with high EI scores had left insular activation when processing fearful faces.
In particular, Antonio Damasio has proposed that this region plays a role in mapping visceral states that are associated with emotional experience, giving rise to conscious feelings.
[citation needed] In terms of function, the insula is believed to process convergent information to produce an emotionally relevant context for sensory experience.
[72] The anterior insular cortex (AIC) is believed to be correlated to emotional sensations, including maternal and romantic love, anger, fear, sadness, happiness, sexual arousal, disgust, aversion, unfairness, inequity, indignation, uncertainty,[73][dubious – discuss] disbelief, social exclusion, trust, empathy, sculptural beauty, a ‘state of union with God’, and hallucinogenic states.
The insula receives information from "homeostatic afferent" sensory pathways via the thalamus and sends output to a number of other limbic-related structures, such as the amygdala, the ventral striatum, and the orbitofrontal cortex, as well as to motor cortices.
[82] This regulation of salience might be particularly important during challenging tasks where attention might fatigue and so cause careless mistakes but if there is too much arousal it risks creating poor performance by turning into anxiety.
[82] Studies have shown that damage or dysfunction in the insular cortex can impair decision-making, emotional regulation, and social behavior.
[84] Clinical data additionally shows that bilateral damage to the insula after ischemic injury or trauma can lead to auditory agnosia.
[88][84] Progressive expressive aphasia is the deterioration of normal language function that causes individuals to lose the ability to communicate fluently while still being able to comprehend single words and intact other non-linguistic cognition.
[90] A number of functional brain imaging studies have shown that the insular cortex is activated when drug users are exposed to environmental cues that trigger cravings.
[92] More recent prospective studies, which overcome this limitation, have corroborated these findings[93][94] This suggests a significant role for the insular cortex in the neurological mechanisms underlying addiction to nicotine and other drugs, and would make this area of the brain a possible target for novel anti-addiction medication.
In addition, this finding suggests that functions mediated by the insula, especially conscious feelings, may be particularly important for maintaining drug addiction, although this view is not represented in any modern research or reviews of the subject.
[95] A recent study in rats by Contreras et al.[96] corroborates these findings by showing that reversible inactivation of the insula disrupts amphetamine conditioned place preference, an animal model of cue-induced drug craving.