CONSCIOUSNESS (AROUSAL)We can try and explain many brain functions in a mechanical way as with our computer simile but as in all the major disciplines of science one eventually comes upon a brick wall :- what is space, time, energy, what initiated the big bang, what was there before it, and in the case of the biological sciences what is consciousness ?. This is the only enigma that remains allowing philosophy to reign over neuroscience. Nevertheless consciousness as we know it cannot exist without a brain and is lost forever in brain disease or brain death. Even our deepest emotions such as love and hate, happiness or deep depression can only exist in the conscious brain. Consciousness is very difficult to define, Descartes dictum "I think therefore I am (Cogito Ergo Sum) falls short in defining consciousness since the converse is not true, if I cant think I may be demented, deluded or hallucinated but I am not unconscious. If unconscious for a prolonged time do I exist as a person with a mind, if for ever unconscious and so brain stem dead do I exist. We all know when we are conscious and aware of self existence and the passage of time and we can recognise consciousness in others based upon their responses. We do not however know what is going on in the conscious mind of another person if they do no communicate with us. It is very difficulty to measure conscious awareness or level of arousal, we know when someone is asleep or awake and absence of sleep wake cycles can be used to define coma. Scales such as the Glasgow coma scale do not in fact measure consciousness but behavioural responses to stimulation. If one gives a non anaesthetised person curare they are fully conscious but how does an outsider determine that there is a personal inner awareness. Is a newborn infant conscious ? most people would agree that it is conscious in that it shows sleep wake cycles and shows arousal to stimuli such as hunger. Is a baby conscious in utero before birth or does consciousness appear at
birth, they certainly show sleep wake cycles in utero, when does that consciousness appear during development of the foetus when brain stem develops, diencephalon or cortex, has it any content ?. Are we conscious in REM sleep when dreaming and immediately aware but memory is switched off so there is usually no recall. Clinical diffrentiation of different disorders with absent responses may be impossible ie. Coma Persistent vegetative state Sleep Anaesthesia or drug overdose Akinetic-mutism Dystonia with non communication An absence seizure or fugue state Brain stem death
No one would doubt that their pet dog or horse was conscious shows recognition and could remember people and places as well as understanding a limited vocabulary ( or intonation pattern). Are all vertebrates conscious, are all animals with a rudimentary cerebral cortex such as a shark or dogfish. Is consciousness, even a microconsciousness a feature of all living cells and a huge protoplastmic conglomerate such as the brain merely amplifies it into a macroconsciousness ?. If consciousness is a feature of all living cells then an amoeba or any individual body cell has microconsciousness and trees would be conscious The brain could amass a large amount of consciousness by joining billions of cells in the form of what Graham Cannon in Manchester used to call "organismal control " and death is simply the permanent loss of this organismal control via the reticular formation and a return to a mass cellular microconsciousness.
Do we simply need a nerve net such as the reticular formation linking millions of cells as one unit to give us consciousness. Does the size of the cerebral cortex merely store more information for the content of consciousness ( a human with gigabytes of cerebral hard disc and a fish or bird megabytes, invertebrates with only a ganglion a kilobyte ? !). Some experts in artificial intelligence have claimed that a computer if made powerful enough would automatically become conscious. Apart from being a frightening concept, the biggest argument against this is that loss of intelligence in man in mental handicap or severe dementia does not mean a proportionate loss of consciousness only diminution in its content.
The idea that consciousness, like self replication, is simply a property of some macromolecules once they achieve a particular size and configuration is as equally frightening as the computer model. It perpetuates the saga of ignoring the whole cell as the unit of life. In neurology we have been obsessed by synapses, neurotransmitters and nerve nets and have forgotten the actual living part of the brain ie the neuron. If we believe that nerve networks achieve consciousness then there would appear to be no sensible reason not to accept that a computers electronic networks could achieve consciousness. We now know that the cell consists of organelles which are themselves as complex as the organs of a whole body one can localise any cellular function to a prescribed sub - cellular unit or organelle. Even accepting this we have completed the circular argument to return to the idea of consciousness being a property that develops in certain self replicating large molecules eg. DNA.
Anatomy of Consciousness
Consciousness depends upon the reticular activating system and septal nuclei being intact. One may have a gross lower brainstem, ie lower pons and medulla, lesion as with a pontine glioma so that all body movement, speech and swallowing are paralysed and yet the child may be fully conscious and can think normally. One may equally remove a whole cerebral hemisphere thus limiting the content of consciousness and yet the child is fully conscious. Extensive disease of both cerebral hemispheres will cause severe mental defect or dementia and so limit or even abolish all cognitive learning (as in post - traumatic persistent vegetative state) and thus grossly restricting the content of consciousness (thought processes) and yet the child is still conscious. That is to say there is a relatively small area of upper brain stem, thalamus and septum which appears to be necessary to sustain consciousness and a small lesion here as with tentorial herniation secondary to raised intracranial pressure, primary midbrain injury in trauma, localised encephalitis or tumour may cause prolonged coma. An irreversible lesion in the brainstem eg central ischaemic neuronal necrosis, can result in permanent failure of cortical arousal and consciousness, hence the concept of brain death depends upon brain stem function rather than cortex.
The mesencephalic reticular formation leads to continuous sleep and lesions in the medullary reticular formation to constant wakefulness. The reticular formation is a continuous network of small interconnected cells which have a basketwork of axons, dendrites and side connections form ascending and descending pathways. The dendrites are long and straight. The axons run upwards and downwards coveing many levels from the same cell. The reticular formation starts caudally in the central grey matter of the spinal cord and is then present in medulla as the medial and lateral reticular nuclei which give rise to the reticulospinal pathways. There are some very
large cells in the medulla and pons ie the gigantocellular nucleus. The midbrain, thalamic reticular nucleus and intralaminar thalamic nuclei all form part of the system There are also the specific neurotransmitter pathways which influence the cerebral cortex and basal ganglia eg. Nor adrenaline from the locus coeruleus Serotonin - from the median raphe nucleus ( plate of neurones in midbrain and pons) Dopaminergic from the substantia nigra Cholinergic from Meynherts nucleus. middle of
Reticular Activating System. Fibres to the cortex arise from the intralaminar thalamic nuclei, locus coeruleus and Raphe nuclei. Possibly switch on specific areas via the cartridge on the apical dendrite. Cuses arousal and wakefulness or vigilance, changes respiration and blood pressure There is tonic activity of the arousal system.
The EEG desynchronises with reticular activating stimulation causes the synchronised slow waves of sleep to disappear with lower amplitude asynchronous fast activity appearing. It takes only 10 seconds of ischaemia to flatten the EEG and impair consciousness but 4 minutes ro irreversibly damage the cortex. Even after reanimation there is often consciousness with sleep wake cycles but little content or communication. Consciousness depends upon energy from oxygenation but is not permanently lost by periods of hypoxia,
Thought is the content of consciousness Short term memory is the capacity of consciousness Attention maintains the current content of consciousness Distraction clears current content.
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No one would doubt that their pet dog or horse was conscious shows recognition and could remember people and places as well as understanding a limited vocabulary ( or intonation pattern). Are all vertebrates conscious, are all animals with a rudimentary cerebral cortex such as a shark or dogfish. Is consciousness, even a microconsciousness a feature of all living cells and a huge protoplastmic conglomerate such as the brain merely amplifies it into a macroconsciousness ?. If consciousness is a feature of all living cells then an amoeba or any individual body cell has microconsciousness and trees would be conscious The brain
could amass a large amount of consciousness by joining billions of cells in the form of what Graham Cannon in Manchester used to call "organismal control " and death is simply the permanent loss of this organismal control via the reticular formation and a return to a mass cellular microconsciousness. Do we simply need a nerve net such as the reticular formation