Mood disorders consciousness

Mood disorders produce impairments in many domains relevant to a debate on the biology of both the subjective and objective components of consciousness. Thus a description of the neurochemistry believed to be important... 

Neuropsychological impairments in mood disorders, particularly those of working memory and executive function, are the most convincing and objective demonstrations of an impairment of consciousness. Since these impairments do not correlate with the severity of the mood disturbance and persist upon recovery they are not simply epiphenomena of the mood disturbance but rather may index trait pathology in susceptible individuals. It has previously been argued that mood disturbance and neuropsychological impairment may result from disturbances in two different neurochemical systems, the serotonin (5-HT) system and the hypothalamic-pituitary-adrenal (HPA) axis, between which there is a close interaction (McAllister-Williams et al., 1998). 

Tryptophan depletion in healthy volunteers impairs the retrieval of learnt material (Park et al., 1994), an effect probably mediated through a selective impairment of episodic memory consolidation (Riedel et al., 1999 Schmitt et al., 2000). However, tryptophan depletion appears to have no effect on working memory (Riedel et al., 1999) and either no effect or an enhancement of tests of executive function (Park et al., 1994 Schmitt et al., 2000). Thus the abnormality in episodic memory in mood disorders could conceivably be related to an impairment in the 5-HT system, but such an impairment is unlikely to account for the abnormalities in working memory and executive function. Clearly then, changes in consciousness occurring in affective disorders are unlikely to be explainable on the basis of an abnormality in a single neurochemical system. 

But while we know in general which parts of the brain are involved in mood, we know very little about how the parts are involved and next to nothing about the details of how the neurological substrates are involved in various moods. And although we know more than we did 50 years ago, we still don t know how mood originates and how it s translated from neural activity to conscious awareness. Nevertheless, we can expect that the parts of the brain involved in mood play some role in mood disorders. 

If affective disorder could be eliminated by the simple expedient of administering a chemical substance, did this not suggest that the basis of these disorders might take a chemical form And not only that might affect, mood, emotion, and the whole gamut of human conscious experience be translated into chemical terms At a stroke, the elusive "aetherial" Freudian psyche was replaced as the primary object of attention by the polyphasic physico-chemical system called the brain. Psychiatry came of age and took its place among the biological sciences. 

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