Home Page Overview Site Map Index Appendix Illustration About Contact Update FAQ

Mulitcellular Organisms


MRI Consciousness is usually defined as the part of the human mind8 that is aware of the feeling, thoughts and surroundings. Actually there is no simple, agreed-upon definition of consciousness. Some working definition(s) will be discussed later. Most of the philosophical discussions of consciousness arose from the mind-body issues posed by Rene' Descartes in the 17th century. He asked: Is the mind, or consciousness, independent of matter? Is consciousness physical or non-physical? It is now recognized that the phenomena by which we define consciousness are correlated with certain configurations of activity in certain nervous systems and not with others. Most neural activity doesn't generate consciousness, even in the supremely conscious human brain. Moreover, the activities that do generate consciousness do not produce it by accident or in a happenstance manner. Consciously processed events in the nervous system have a very clear physical signature, in the form of characteristic brain activity. There is good empirical evidence that consciously registered events leave distinct traces in the brain and are processed in special ways within the brain's networks. Techniques such as EEG, f MRI, and PET provide information about the relationship between mental tasks and the collective activities of groups of many millions of neurons (see Figure 10-26). In stark contrast to this, electrodes have been developed

Figure 10-26 Activities and Mental Tasks

which are so fine that their tips can be inserted into single cells so that the firings of individual neurons in some brain location can be monitored. It is possible to see how an individual neuron reacts when an animal is looking at an object moving sideways, or seeing the colour blue, or
planning an action, ... The study of consciousness used to be relegated to the fringe of science until recently in the 2000's when more reliable tools have been developed to probe the innards of the brain. The problem is how to bridge the objective world of physical matter to the subjective world of sentience. The magnitude of the task is similar to understand how a collection of lifeless materials would become a living entity, i.e., the origin of life.

Consciousness Sigmund Freud (1856-1939), the founder of psychoanalysis, compared the human mind to an iceberg. The tip above the water represents consciousness, and the vast region below the surface symbolizes the unconscious mind. This subconscious mind is the sum total of our past experiences. What we feel, think, or do forms the basis of our experience. These experiences are stored in the form of subtle impressions in our subconscious mind. These impressions interact with one another and create tendencies. The resultant of these tendencies determines our character (see Figure 10-27a). However, if the unconsicous drives (the id) might prompt behavior that would be incompatible with our civilized conception of ourselves, the action would be suppressed by the conscious mind (the ego). In the "talking cure" (the practice of psychoanalysis) the patient is helped by the therapist, who takes notice of the mental lapses, interpret the unconscious struggles they reflect and bring them into the light of self-awareness. Because of the subjective overtone, this Freudian concept has been fallen out of favour by 1950s. Better understanding of brain chemistry gradually replaced his model with a biological explanation of how the mind arises from neuronal activity. But since mid 1990s, attempts to piece together diverse neurological findings have validated the general

Figure 10-27a Consciousness [view large image]

sketch Freud made almost a century ago. The lower diagram in Figure 10-27a identifies some Freudian terminologies with the modern anatomy of the human brain. The overlapping disciplines of psychoanalysis
and neuroscience is the growing movement of neuropsychoanalysis. One of its subjects of study is depression. It is posited that the problem is related to the emotional attachment of the baby. Mother's care-taking is a life-or-death matter for the mammalian babies, who are born helpless. Such neuro-circuit remains in the background even when the babies have grown up. The pain of separation from something triggers such helpless feeling for some individuals and manifests as depression.

Habit Forming Conscious processing is slow, expensive and subject to error. The unconscious version develops gradually from such clumsy beginning in the frontal cortex. If the same kind of routines is performed repeatedly, processing is transferred to the striatum to run the task automatically (Figure 10-27b). Habit is formed by the secretion of dopamine which induces pleasurable sensation or some kind of reward leading to the desire for repeating the experience. In this way, the work will be completed faster, more effectively and at a lower metabolic level to conserve energy. It includes a whole range of neural processing from the automatic reflex of some simple animals such as the E. coli (in seeking food and avoiding danger) to automatic actions taken by human. There are good and bad habits. They are difficult to get rid of once established firmly such as in drug addiction. One way to get a handle on bad habits is to become aware of them. Then focus the attention on the problem to help the frontal cortex to resist the call of the autopilot. The habit will fade away if it is not practised for a long time.

Figure 10-27b Habit Forming [view large image]

Conscious Controllers Figure 10-27c presents a modern view of the conscious. It divides the conscious and subconscious thought into four divisions (controllers). While the Pavlovian controller is the brain's autopilot, the other three control systems (see more detail in the diagrams, and brain components) combine both kinds of thought to achieve the best possible outcome depending on the level of uncertainty about the situation you are in. In this model, subconscious and conscious thoughts are more like equal partners than competitors. The two work together to evaluate all the available information whether consciously or subconsciously perceived. Our behaviour is often driven by more than one of the four controllers. This is especially true when we are learning something new where the balance between ignorance and experience changes. Importantly, the subconscious isn't the dumb cousin of the conscious, but rather a cousin with different skills.

Figure 10-27c Conscious Controllers [view large image]

Two competing models emerge in 2007 to link the brain's activity with subjective experience (consciousness). The Qualitative model suggests that a coalition of pyramidal neurons (a special kind of neurons) linking the back and front of the
NCC Models cortex fires in a unique way. Different coalitions activate to represent different stimuli from the senses (Figure 10-28e). The Quantitative model maintains that neurons across the brain fire in synchrony and prevail until a second stimulus prompts a different assembly to arise. Various assemblies coalesce and disband moment to moment, while incorporating feedback from the body. Stronger external stimuli engage larger number of neurons and trigger higher degree of consciousness (Figure 10-28e). These models have not addressed the all-important middle step of how a

Figure 10-28e NCC Models
[view large image]

phenomenon causes an experience. They have not explained how consciousness arise, i.e., how physiological events in the brain translate into what is experienced as consciousness (dubbed as the "hard problem").

    By implanting electrodes in the brains of 10 volunteers with drug-resistant epilepsy, a study in 2009 reports that the signature of consciousness involves:
  1. During the first 30 milliseconds of the experiment, brain activity involving the non-conscious and conscious tasks was very similar, indicating that the process of consciousness had not kicked in.
  2. There is an increase in the voltage levels of the signals in the brains after the first 30 milliseconds.
  3. The frequency and phase of neurons firing in different parts of the brain become synchronize.
  4. Some of these synchronized signals appear to be triggering others.
  5. This study suggests that consciousness has no single seat. It is more a question of dynamics than of local activity.

Recently in 2007, it is suggested that all the above are "red herrings". Consciousness does not depend on language as babies, and many animals are not insensate robots. Nor can consciousness be equated with self-awareness. At times we have all lost ourselves in music, exercise or sensual pleasure, but that is different from being knocked out cold. Even the central control architecture is an illusion. Consciousness turns out to consist of a maelstrom of events distributed across the brain. These events compete for attention, and as one process out-shouts the others, the brain rationalizes the outcome after the fact and concocts the impression that a single self was in charge all along.

Global Workspace Models According to the global workspace model of consciousness, the unconscious brain is always active. But at the moment of crossing into consciousness, the level suddenly becomes a lot more intensive and spreads into a much wider area of the brain (Figure 10-28f). The theory is supported by an experiment in 2014. It is suggested that the brain always maintains a lower level activity involving many tasks until the arrival of one particularly relevant event which triggers the collection of all the related information from different parts of the brain. This theory is consistent with the observation of default state, it may also relate to the notion of subconscious mind in the Freudian era.

Figure 10-28f Global Workspace Model [view large image]

8Mind is defined as the mental activity, which includes both conscious and unconscious processes, thus mind has a broader meaning than consciousness.

See "Origin of Consciousness - Integrated Information Theory (IIT)" for recent development in the study of consciousness.

Go to Next Section
 or to Top of Page to Select
 or to Main Menu