Autonomic Nervous System: Arousal


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Autonomic Nervous System

Cardovascular activity

Electrodermal activity

References


 

Autonomic Nervous System


The main function of the autonomic nervous system (ANS) is the adaptation of an organism’s internal state to changes in the environment. The autonomic nervous system innervates every organ in the body, and accordingly, can modulate sensory, visceral, motor, and neuroendocrine functions. It functions independently (autonomously) and continuously, without conscious effort. The ANS is controlled by brain areas such as the anterior cingulate cortex, the insula, the amygdala, and the hippocampus (Critchley et al., 2002, 2003; Matthews et al., 2004). The neurotransmitters involved in autonomic activity comprise the cholinergic and noradrenergic pathways, and the nuclei releasing these neurotransmitters are the locus coeruleus and the basal nucleus of Meynert.
The autonomic nervous system can be subdivided into two major components: the sympathetic and the parasympathetic branches. The parasympathetic nervous system can be viewed as a restful or energy-conserving division of the autonomic nervous system, which is most active under ordinary, restful and digestive conditions. It also counterbalances the effects of the sympathetic part, and restores the body to a resting state following a stressful experience. The sympathetic nervous system activates body processes with the aim to create an attentive state in which one is able to ‘fight and flight’. The sympathetic nervous system acts to increase output in certain emotional situations or extreme levels of exercise, and can be viewed as a mobilising and energy boosting division of the autonomic nervous system. In a healthy nervous system these branches of the autonomic nervous system are collaborating to maintain or create an optimal metabolic state, which is necessary given a particular action or environment. Therefore, the activity of the autonomic nervous system refers to the internal state of arousal, vigilance, alertness, and even cognitive information processing. The functioning of the ANS can be assessed by measuring cardiovascular and electrodermal activity.

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Cardovascular activity


Environmental input of different quality (e.g. emotional, cognitive stimulation) can activate different parts of the brain causing particular variations in heart beat. The brain areas involved in cardiovascular functioning are mostly located in the frontal cortex and include parts of the cingulated cortex, the insular cortex and the orbitofrontal cortex (Mesulam, 1983). Heart rate variability (HRV) can be used for measuring the function of both branches of the ANS, because the sympathetic and parasympathetic branches each make distinguishable frequency-specific contributions to the heart rate power spectrum (Mulder, 1992). Slow variations of the heart rate mainly reflect the influence of homeostatic control processes, mediated by the sympathetic branch of the ANS (Berntson et al., 1997). More rapid fluctuations reflect processes related to blood pressure, controlled predominantly, but not exclusively, by the sympathetic branch of the ANS (Akselrod et al., 1981). Very fast fluctuations are related to respiratory activity, primarily controlled by the parasympathetic branch of the ANS (Akselrod et al., 1981; Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996). In addition, the balance between both branches of the ANS can be examined using HRV (Malliani et al., 1998; Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996). This so-called sympathovagal balance reflects the overall state of the autonomic nervous system resulting from both the sympathetic and parasympathetic influences (Eckberg, 1997). Together, these measures were used to examine the state of arousal in the patients of our studies.

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Electrodermal activity


Electrodermal activity (EDA) is thought to reflect attention to new information in the environment, and some elementary forms of learning (habituation – decreasing reaction intensity with repeated stimulation), memory storage and retrieval (Boucsein, 1993). Although not fully understood, electrodermal activity (EDA) can be elicited by at least three different, but interconnected central pathways: a premotor cortical-spinal system, a limbic-hypothalamic system, and pathways involving the reticular formation (Dawson et al., 2000). Different environmental stimuli can activate different parts of the brain to cause electrodermal reactivity to occur. The ipsilateral limbic system primarily controls electrodermal activity in response to emotional and affective situations, whereas the contralateral system is critical in controlling electrodermal activity during orienting and cognition.
Electrodermal activity is highly influenced by the sympathetic part of the autonomic nervous system. Human sweat glands have predominately sympathetic cholinergic innervation from sudomotor fibres originating in the sympathetic chain, and some adrenergic fibres also exist in close proximity (Shields, 1983).

 


References

Akselrod S, Gordon D, Ubel FA, Shannon DC, Barger AC, Cohen RJ. Power spectrum analysis of heart rate fluctuation: a quantitative probe of beat-to-beat cardiovascular control. Science 1981; 213: 220-222.

Berntson GG, Bigger JT, Eckberg DL, Grossman P, Kaufmann PG, Malik M, et al. Heart rate variability: origins, methods, and interpretive caveats. Psychophysiology 1997; 34: 623-648.

Boucsein W. Methodological issues in electrodermal measurement. In: Roy JC, Boucsein W, Fowles DC and Gruzelier JH, editors. Progress in electrodermal research. New York: Plenum Press, 1993: 31-41.

Critchley HD, Mathias CJ, Dolan RJ. Fear conditioning in humans: the influence of awareness and autonomic arousal on functional neuroanatomy. Neuron 2002; 33: 653-663.

Critchley HD, Mathias CJ, Josephs O, O'Doherty J, Zanini S, Dewar BK, et al. Human cingulate cortex and autonomic control: converging neuroimaging and clinical evidence. Brain 2003; 126: 2139-2152.

Dawson ME, Schell AM, Filion DL. The electrodermal system. In: Cacioppo JT, Tassinary LG and Berntson GG, editors. Handbook of psychophysiology. Cambridge: Cambridge University Press, 2000: 200-223.

Eckberg DL. Sympathovagal balance: a critical appraisal. Circulation 1997; 96: 3224-3232.

Malliani A, Pagani M, Montano N, Mela GS. Sympathovagal balance: a reappraisal. Circulation 1998; 98: 2640-2643.

Matthews SC, Paulus MP, Simmons AN, Nelesen RA, Dimsdale JE. Functional subdivisions within anterior cingulate cortex and their relationship to autonomic nervous system function. Neuroimage 2004; 22: 1151-1156.

Mesulam MM. The functional anatomy and hemispheric specialization for directed attention. The role of the parietal lobe and its connectivity. Trends in Neurosciences 1983: 384-387.

Mulder LJM. Measurement and analysis methods of heart rate and respiration for use in applied environments. Biological Psychology 1992; 34: 205-236.

Shields SA. Development of autonomic nervous system responsitivity in children: a review of the literature. International Journal of Behavioral Development 1983; 6: 291-319.

Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Circulation 1996; 93: 1043-65.