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Neural integrationNeural mechanisms of autonomic, affective and cognitive integration Hugo D. Critchley, Wellcome and UCL Journal of Comparitive Neurology, 493, pp. 154-6 INTRODUCTION: This paper discusses evidence for the involvement of bodily responses in brain processes, particularly those related to emotional experience. There does, however, seem to be 'a dog that doesn't bark in the night' somewhere in this paper. There seems to be an unspoken assumption that there is an important distinction between volitional or motivational actions and unconscious activity, and also an assumption that subjective emotions are somehow important to the former. This of course flies in the face of the rigid orthodoxy of psychology and most neuroscience to the effect this distinction is an illusion, and that subjective emotions and other experience are of little scientific relevance. An additional problem in reading this paper is that it is not clear whether the author thinks that all emotional experience is derived from bodily sensations or only some. While the studies discussed in the paper certainly support the latter, the former looks less plausible. This paper discusses studies that support the view that bodily processes act on brain processes, and are important in the generation of the subjective experience of emotions. Specific brain areas are highlighted in respect to brain-body interaction and emotion. The anterior cingulate cortex is seen as being involved in generating responses by the autonomic (involuntary) parts of the nervous system, while the insula and orbitofrontal cortex are thought likely to map the visceral (internal organs) responses. The ventromedial prefrontal cortex supports states of rest that may serve as a benchmark for more dynamic activity. The interaction of the anterior cingulate, the insula and the orbitofrontal are suggested as possibly being the basis for emotional experience and motivated behaviour. Generation of and subsequent feedback from autonomic processes is suggested to be linked to subjective emotions. The autonomic nervous system is the mainly regulator of bodily functions, and allows responses to environmental changes. The autonomic system is divided into the sympathetic and the parasympathetic system. The sympathetic system relates to motor action and changes such as heart rate that relate to motor action, and it is thus associated with 'fight and flight reactions'. The parasympathetic system is involved with recuperative processes, such as reducing the heart rate. The sympathetic system originates in the brain stem, and extends down down the spine and utilises adrenaline and noradrenaline as transmitters. The parasympathetic also originates from the brain stem and uses acetylcholine as a transmitter. The sympathetic system is also acted on by nuclei in the hypothalamus. Experiments have demonstrated influences on the autonomic system from the cingulate, the insula and the medial temporal lobe via both the hypothalamus and the brain stem. However, the brain stem's autonomic centres require feedback from the body to maintain homeostasis (stable conditions in the body). This feedback also influences motivational behaviour by conveying information on levels of comfort or discomfort. In support of Damasio's somatic marker theory, the experience of feedback from bodily states is hypothesised to be the basis of the subjective experience of emotion. This argument seems sound up to a point, but it is difficult to think that external stimuli, especially the more urgent ones, for instances phobic fear reactions, cannot occur without being laboriously processed through internal organs. The same qualification could apply to emotions arising from cognitive activity. Again it seems laborious and maladaptive in terms of use of energy for everything to have to go via the internal organs, before it can be assessed in terms of emotional experience. Another objection dating back to the 1920s is that bodily arousal is too limited in its range to account for all the variations in subjective emotional experience. The impairment of judgment, decision taking and behaviour in patients with orbitofrontal and ventral prefrontal damage is seen as supportive of the somatic marker idea, but at least some of the deficits here can also be viewed as a consequence of impaired communication between the frontal and limbic areas of the brain. The finding that autonomic arousal is reduced in patients with lesions does not seem that surprising, as outward as well as inward signaling is likely to be impaired by the lesions in the brain. In particular, this does not seem enough to support Damasio's rather vague notion of the self arising from representations of the body state. This is not to say that the body plays no part in it, but it would seem to require considerably more evidence to suggest that the body by itself creates the self. The evidence of studies indicates that the hypothalamus monitors the body, and that sensory information from the body projects to viscosensory cortex in the insula and the orbitofrontal. In primates this information does not go via a structure in the pons area of the brain stem, and this would seem to be indicative of a less automatic system than in other animals. Similarly, sympathetic arousal of skin conductance has been shown to enhance activity in the ventromedial prefrontal, the right anterior insula and the dorsal anterior cingulate. The dorsal anterior cingulate is seen as a brain area of particular interest because it is involved in attention and cognitively demanding activities. Researchers have considered that it may have a role in executive control and possibly consciousness. There is a correlation between dorsal anterior cingulate activity and task difficulty, and this type of mental stress enhances sympathetic activity. It is claimed that various studies argue in favour of the dorsal anterior cingulate having control over the autonomic system during volitional behaviour, including difficult cognitive activity. The amygdala and particularly the central nucleus of the amygdala is also seen to produce autonomic arousal when it is receiving emotional stimuli. The dorsal anterior cingulate and the amygdala are often active at the same time. The activity of the dorsal anterior cingulate during volitional behaviour may provide control over the autonomic system. Also visceral and pain stimuli are associated with enhanced activity in the anterior cingulate, insula and thalamus. The dorsal pons in the brain stem and the anterior cingulate are both sensitive to any absence of feed back from the body. The mid-insula and the amygdala are sensitive to autonomic arousal as a result of emotional stimuli, and this is taken to suggest a role for the right insula in the experience of emotion. Activity in the right anterior insula predicts subjective emotional experience and is also connected to visceral activity. Generation of autonomic responses may originate in the anterior cingulate during volitional and cognitive activity, while the conscious experience of visceral responses and subjective emotion may arise in the anterior insula, especially the right anterior insula. The insula and the anterior cingulate are often active at the same time in the event of pain, threat or attention. The activity of the dorsal anterior cingulate predicts autonomic arousal. Other research emphasises the importance of the anterior cingulate in cognitive control. The anterior cingulate is important for monitoring actions and their consequences and also performance errors. The anterior cingulate and the amygdala generate and map bodily responses that are interconnected with the orbitomedial region. The intensity of bodily responses is suggested to have an influence on subjective emotion. |
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