11.5 Factors that affect the contents of phenomenal consciousness

Electro-magnetic stimulation

Since the early proposals that the nervous system operates with electrical signals there have been many attempts to affect brain functions by electrical stimulation. The initial efforts in the 19^th Century aimed at establishing whether there is a localisation of sensory and motor functions that could be revealed with the stimulation of specific sites in the brain. Studies continued in the 20^th Century and eventually completed the mapping of the sensory–motor cerebral cortices according to the location of the sensory inputs and of the motor outputs that controlled somatic function, leading to the well established sensory and motor “homunculi”. The task was completed at the time of Wilder Penfield, a neurosurgeon who made such maps as a way to spare as much brain tissue as possible during neurosurgical operations¹. 

Interestingly, electrical brain stimulation carried out during neurosurgery demonstrated that is difficult to directly elicit experiences by stimulating the frontal lobes, whereas it was easier to trigger specific experiences by stimulating the posterior cortex. After reviewing these results in the context of work over last hundred years, it has been concluded that “the modulation of activity within a localized, but distributed, neuroanatomical network might explain the perceptual and behavioral phenomena that are reported during focal electrical stimulation of the human brain”². For example, stimulation of the parietal cortex in human subjects can generate perception of faces³. Very convincing evidence that localised cortical areas can elicit very subjective specific feeling, for example of wanting to move a limb, was provided by Desmurget and collaborators⁴. Electrical stimulation of specific regions of exposed cortical surface, result in a hallucinatory experience of hearing music⁵.

However, subsequent experiments with stimulation of regions of the prefrontal cortex, orbitofrontal cortex and anterior cingulate cortex in some cases altered reports of self-awareness⁶. Furthermore, intracranial electrical stimulation of certain prefrontal regions (i.e., orbitofrontal cortex and anterior cingulate cortex) can reliably perturb conscious experience⁷.

Deep brain stimulation of subcortical brain structures, such as the extended reticulothalamic activating system and periaqueductal grey, and of the limbic circuits arising from them, generates powerful affective responses.⁸

From these few examples, it is beyond doubt that states of consciousness can be modified by localised direct electromagnetic stimulation of the cortex.

Effects of specific chemicals on states of consciousness 

Several natural and synthetic chemicals have profound effects on perceptive, cognitive, or affective conscious states. Generically these substances are called psychotropic, psychedelic, or hallucinogenic drugs. Many of these substances have been extracted from plants and have been used in most cultures in cultural and religious ceremonies for millennia. Some have been synthesised more recently.

Most these drugs act on the nervous system by acting on specific neurotransmitter mechanisms which are involved in normal brain functions. Common neurotransmitter systems that are affected include noradrenaline (norepinephrine), dopamine, serotonin (5HT), acetylcholine, glutamate, endocannabinoids, and neuropeptides. The drug-mind interaction indicates an intimate connection between the brain and the mind⁹.

The following is a brief overview of some of these drugs and their effects.

Drugs that affect serotonin, noradrenaline, and dopamine and are mostly hallucinogenics. Hallucinogenic substances produce deep changes in the perception of reality. They affect the very processes underlying the making and maintenance of a self with a sense of being in a real world within the fundamental Kantian categories of space and time. As a result, depersonalisation (“ego dissolution“) may occur. Hallucinations including hearing voices and having visions are common consequences of administration psychotropic drugs. Similar experiences also occur in extreme ascetic lifestyle of monks and gurus with food and water deprivation. The use of psychoactive substances has been often linked to spiritual beliefs and has become part of some religious ceremonies. 

The Peyotl cactus (peyote) contains the alkaloid mescaline which acts on catecholamine receptors and used in religious ceremonies by Mexican and North American indigenous people. The ‘San Pedro’ cactus also contains mescaline and has been used in Peru in pre-Inca cultures.

Drugs that affect serotonin mechanisms include ayahuasca, a Peruvian Quechua word meaning ‘wine of death’, used for centuries by indigenous peoples from regions of the Andes and of the Amazon basin including Peru, Argentina, Brazil, Colombia and Ecuador for religious rituals. The active chemical extracted from the plant Banipsteriopsis is DMT (dimethyltryptamine). DMT is also contained in the hallucinogenic drug known as yopo (from Anaderanrthera peregrina) used by indigenous people in the Orinoco forests. It has been proposed that endogenous DMT is involved in near death experiences¹⁰.

Psylocybin a tryptamine derivative similar to DMT extracted from magic mushrooms (Psylocibe, Teonanacatl), or the plant Oliluqui (Morning Glory), used in central America and in Europe. Although western medicine has explored the scientific value and therapeutic potential of psychedelic compounds for over a century, there has been a recent resurgence in the potential use of natural psychotropic drugs in psychiatric disorders including psylocybin.

Ergot alkaloids which act on serotonin mechanisms include derivatives of lysergic acid from Claviceps purpurea, a parasitic fungus of the rye grain used in the Middle Ages for bread making. Following ergot poisoning, Medieval Europeans suffered collective mental derangements known as St Anthony Fire and possession by witches. Such incidents were believed to be due to spiritual experiences of some afterlife. Ergot poisonings were involved in the Eleusinian mysteries in ancient Greece.

The best known semi‐synthetic ergot alkaloid is the lysergic acid diethylamide (LSD). This compound, first synthesised accidentally by Albert Hofmann in 1938, is the most potent hallucinogen known. 

Cocaine (from Peruvian Quechua: kúka) is a tropane alkaloid from the Coca plant (Erythroxylum spp) used by Indigenous South Americans for its psychoactive effects. It acts by increasing the levels of the neurotransmitters dopamine, serotonin and noradrenaline at their synapses in several neural circuits including those for rewards and pleasure. In the short term, this leads to euphoric and anti-depressive effects, often accompanied by a feeling of loss of connection to reality.

Ecstasy (3,4-Methyl-enedioxy-methamphetamine; MDMA) is a potent synthetic stimulant primarily used for recreational purposes. It acts primarily by releasing endogenous dopamine involved in reward circuits within the brain. Its desired effects include euphoric rush with altered sensations including an altered sense of time, empathy, and relaxed pleasure.However, side effects include high blood pressure, accelerated heartbeat, and severely raised body temperature. In many respects, these actions are similar to those of cocaine.

Drugs that affect acetylcholine function have beed derived from diverse plants including deadly nightshade (Atropa belladonna), its relatives datura and Brugmansia; mandrake; and fly agaric mushrooms. The primary active ingredient is all these plants is an antagonist to the muscarinic receptors for acetylcholine. Derivative of these compounds are used medically to prevent nausea and vomiting caused by motion sickness or medications used during surgery. However they also elicit hallucinations, accompanied by confusion, delusions, excitement, and irritability.

Tobacco has long been used in the Americas, with some cultivation sites in Mexico dating back to 1400–1000 BC. It was smoked both socially and ceremonially. It acts the nicotinic subclass of receptors for acetylcholine.

Ibogaine is a naturally occurring psychoactive substance found in plants in the Apocynaceae family known as dogbanes for their poisonous qualities. It is a psychedelic with dissociative properties probably due to its actions on wide range of transmitter systems.

Glutamate (glutamic acid) is the primary excitatory neurotransmitter in the central nervous system, acting on a diverse range of receptors. A range of glutamate antagonists, including ketamine, phencyclidine (PCP, Angel Dust) and dextromethorphan, have strong dissociative and hallucinatory actions. All these drugs can have severe side effects ranging from psychosis to anaethesia¹¹.

GABA (γ-aminobutyric acid) is the most widespread inhibitory neurotransmitter in the brain. Natural agonists of its GABA_A receptors include muscimol from the fly agaric mushroom (Amanita muscaria). Muscimol displays sedative-hypnotic, depressant and hallucinogenic psychoactivity.

The use of ethanol, usually derived from the fermentation of sugars by yeast, is widespread and deeply embedded in diverse cultural practices. Ethanol primarily acts as both a euphoric and a depressant, causing sedation, relaxation, and decreased anxiety. Its mechanisms of action are complex, and include modulation of the functions of many different classes of neurotransmitter receptors.

The primary psychoactive compound in cannabis (marijuana, hashish, derived from hemp, Cannabis sativa) is tetrahydrocannabinol (THC). THC acts on CB1 receptors with short-term effects that may include a general altered state of consciousness, euphoria, relaxation or stress reduction.

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Initiated by the discovery of mescaline, catalysed by the synthesis of LSD, Western medicine has explored the scientific value and therapeutic potential of psychedelic compounds for over a century. The return to using natural psychotropic drugs in medicine has its limitations. Giving exogenous psychotropic drugs is equivalent to flooding the brain with little target precision. Since neurotransmitters and their receptors are present in different neural circuits, drugs given as a rain are bound to have multiple parallel effects depending on the anatomical distribution of their specific receptors in the different neural circuits of the brain. Developing pharmacological agents acting more selectively on specific subclasses of receptors would be more appropriate.

A good example of the lack of precision and consequent multiple side-effects is the use of opiates such as morphine and heroin. Opioid receptors are present in different brain circuits including those mediating pain control, sleep, and respiration. Exogenous opiates are usually used in medicine to reduce pain but they unavoidably also activate rewards mechanisms resulting in tolerance and dependence.

The observations that pharmacological agents affect states of mind show that there is an indisputable relation between changes in the electrochemistry of the brain and mental states. But this is well accepted. My implication is that more precise interventions on specific levels of the multistorey neural binding will clarify the exact nature of the physical bases for those states.

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