Consciousness - An Introduction (ch10)

How do the brain and consciousness interact with each other? - Chapter 10

Some people believe that we can understand consciousness if we can capture brain activity in more detail. Others believe that we can never understand consciousness. The question, of course, is how consciousness is related to the brain. To answer this question, a certain kind of research can be used, namely the research into 'the neural correlates of consciousness' (NCC). In this way aspects of neural functioning can be studied and it can be checked whether these correspond to the conscious experiences that people express. Unfortunately, it is not yet clear what aspect of neural functioning should be investigated for this. It is important to remember that the NCC is about the correlation between neural functioning and conscious experiences. Therefore, no statements can be made on the basis of NCC about cause-effect relationships between the brain and consciousness.

The human brain

A human brain consists of 100 trillion neurons connected to each other by synapses together with glial cells. The brainstem, consisting of the medulla, punch and midbrain, is essential for survival because it performs many important functions (cardiac, respiratory and sexual functions and the maintenance of sleep and waking). Behind the midbrain is the cerebellum that has an important function in motor control. Between the midbrain and the cerebellum is the thalamus that receives sensory input.

The cortex is the outer layer of the brain and contains many structures that play a role in consciousness - the hippocampus, the amygdala, the hypothalamus and the cingulate gyrus. The neocortex is the part of the brain that developed last during human evolution. The two hemispheres are related to each other by white matter from the anterior commissure and by the corpus callosum.

Unconsciousness

The definition of an 'unconscious person' is someone who lives but is not responsive. For example, people under narcosis are insensitive to pain, but are also unable to respond or communicate.

In experiments it becomes clear which brain regions have to be stimulated to trigger reactions. In patients with PVS, activity occurred in the brainstem, thalamus and the 'primary somatosensory cortex' but not higher in the parietal lobes and 'anterior cingulate cortex'. Giving an anesthetic before the start of an operation also makes someone unconscious for a while. This person then feels no pain and does not know what happened after he or she woke up. Many types of drugs also have different influences on the functioning of humans.

Drugs can be divided into three groups:

1. drugs that weaken responsiveness,

2. drugs that cause memory loss, and

3. drugs that function as muscle relaxants. There is no specific part of the brain where all drugs (that go hand in hand with a form of unconsciousness) act on. Unfortunately, studying the absence of consciousness does not clarify what consciousness is exactly.

There are two theories that have been used to find the NICC. The first theory is from Penrose and Hameroff about the quantum coherence in microtubules. The second theory came from Flohr. He argues that outside awareness caused by drugs is caused by the inhibition of processes that depend on NMDA receptors.

He also states that consciousness depends on the occurrence of so-called 'higher-order self-reflexive representations'.

He drew up the 'representational theory of consciousness' on the basis of his statements. This theory states that states of consciousness occur when someone is in a certain cognitive state. When someone is aware of something, a mental representation is accompanied by a higher order representation for which the functioning of NMDA synapses is necessary.

Conscious vision

Crick wonders what neural data goes hand in hand with conscious vision. Crick admits that no one has been able to capture a brain area so far in which neural activity corresponds exactly to the image we have of the outside world. He does state that conscious vision seems to be associated with the thalamic connections within the cortex. Other scientists have other ideas about this. For example, Ramachandran thinks that the functioning of the temporal lobes provides conscious vision. Crick is looking for a specific part of the brain to which he can link conscious vision, but this can be a wrong starting point. Perhaps no specific place can be found that corresponds to conscious vision.

Competition and awareness

'binocular rivalry' occurs when different images are shown on both eyes. In that case, the images are not combined into an image. There is, however, a form of perception that, is always between the two images. This creates a new form of perception. We get the feeling that both images compete to enter our consciousness.

Research showed that there was increased activity in the occipital-temporal parts of the ventral route. In addition, increased activity was found in the parietal and frontal cortex. This fact provides evidence for the fact that conscious visual experiences are not related to parts of the sensory routes, but more to the central parts of the brain.

Koch finds on the basis of this fact that we are not aware of the early processing in sensory perception, but of the later processing. However, we still know little on the basis of this type of research results. Correlations are only used in the surveys, so no reasons and consequences should be mentioned. In addition, it is still not clear how conscious visual experiences are related to activity in the brain.

Pain

Pain is a subjective feeling. We can not show pain sensations to each other or clarify each other, because pain is mainly linked to feeling. Pain can, however, be found in the body.

When someone is injured, all kinds of changes take place in the body. For example, signals are transmitted by means of thin, unmyelinated neurons (c-fibers) to the spinal cord, brainstem, thalamus and parts of the cortex. The question is, of course, whether neural activity causes the pain experience or whether pain perception causes the neural activity.

Dualists state that pain is in the mind and therefore can not be localized. Damasio believes that having a self is necessary to experience pain. Humphrey states that sensory awareness is an activity. So if you feel pain, you do not remain passive. You try to do something to get rid of the pain. According to him, the perception of pain causes a form of pain perception and this feeling again ensures that we try to do everything to get rid of the pain.

How pain is inflicted appears to make a difference in neural activity. We all know that pain feels different when it is unexpected than when you bring it yourself. It is even worse if you are afraid of it beforehand. External pain causes activity in the posterior ACC (anterior cingulate cortex). This activity does not occur in self-inflicted pain. In the case of activity in the perigenual ACC, the opposite takes place. So there is a correlation between the type of pain and neural activity - and also between the degree to which someone experiences pain and neural activity.

Resources: Blackmore; Susan. (2010). Consciousness, Second Edition An Introduction. Abingdon, Oxon: Taylor & Francis.