Today, there is a widespread consensus that the operations of the conscious mind, encompassing thoughts, perceptions, and emotional awareness, are intricately connected to physiological processes occurring in the brain. But neuroscientists are only just beginning to discover how the activity of brain cells translates into the rich and multi-faceted experience of consciousness.
Whenever you are conscious, your brain cells – the neurons – are active, signaling their neighbors with regular electrochemical pulses. However, this activity is not enough to explain consciousness in terms of brain activity. Even simple studies of brain activity show that neurons also fire when you are in deep sleep. Conversely, even when you are intensely conscious, most of the neural activity in your brain is linked to unconscious processing.
Imagine, for example, that you are sitting in a room reading a good book. The story is compelling, and your conscious mind is filled with the action in the ‘virtual’ world created by your imagination. You are only dimly aware of your real surroundings – the room you are in, the hum of traffic outside, the feel of the book in your hand. And most remarkably, you are not even conscious of the process of reading. Yet, all the time, your brain is processing information about these things. Millions of firing neurons tell your hand how much pressure to exert to hold the book steady. Other nerve cells perceive the shapes of the letters, discern their patterns, and extract their symbolic meanings. Others still notice if anything in your environment changes, for example if someone enters the room.
If your brain works this hard even when you are not conscious, what is so special about the neural activity of the conscious state? To answer this question, we first need to look at how the brain is organized.
Creating conscious perceptions
The human brain consists of a vast network of interconnected neurons, each responsible for processing specific types of information, such as emotions, sensory inputs, memory, language, and more. Within these sub-networks, individual neurons are further specialized for narrow tasks. For example, in the visual system, certain cells exclusively respond to the color red. The intricate complexity of human thought and emotions, collectively referred to as our conscious experience, emerges through interactions among these sub-networks.
One theory proposed by Francis Crick, known for his pioneering work with DNA, suggests how information is processed within this network. Imagine an object, like a grapefruit, positioned in a person’s left visual field. Neurons associated with this information begin to activate, including those responsive to the color yellow and those tuned to round shapes. If the person, whom we’ll call Susan, is initially not paying attention to the grapefruit while watching television, the “yellow” and “round” neurons fire relatively slowly and fade quickly, not contributing to her conscious awareness.
However, when the grapefruit suddenly captures Susan’s attention, these neurons become highly active, firing rapidly. When they synchronize their firing at approximately 40 times per second (40Hz), the “yellow” neurons detect the heightened activity of the “round” neurons, leading to the integration of information. This integration results in Susan perceiving the “grapefruit” rather than merely “yellow” and “round.” As long as Susan remains focused on the grapefruit, messages continue to be exchanged between these neuron groups. If this synchrony persists for about a fifth of a second, Susan becomes consciously aware of the grapefruit. However, if the synchrony dissipates more quickly, the perception does not reach her consciousness despite her brain processing the information unconsciously. This type of perception is referred to as “subliminal.”
Attention and consciousness
Therefore, in order to have complete awareness of something and to be able to recall that it occurred, we must direct our attention to it. Attention can be likened to a searchlight; it concentrates the brain’s resources on a specific area within the vast field of information by intensifying the activity of neurons associated with that area. As we concentrate on one thing, other perceptions fade from our conscious awareness. The spotlight of attention is never still, so these patches of highlighted activity keep changing: at one moment, the grapefruit is privileged, but soon, nothing else takes its place. Other things may be relegated to the half-light of subliminal experience or go entirely unnoted.
The central self
The focus of attention shifts constantly, yet our perceptions are woven together to form our individual experiences of the present moment. This feeling of a “self” at the center of our perception is a vital element of conscious awareness. While the brain mechanisms responsible for this self-awareness remain incompletely understood, they appear to be located within a neural circuit connecting the frontal lobes, responsible for abstract thinking, with the language centers of the left hemisphere. This circuit weaves an ongoing narrative — the narrative self. As long as this narrative unfolds, the experience can seamlessly merge into the current stream of consciousness. But when these circuits are inactive, information processing in other areas of the brain ceases to be ‘ow ned’ by the individual and, therefore, cannot be described. The self-system creates such a strong feeling of unity that it is generally assumed that one brain can hold just one consciousness. However, some theorists believe that micro-consciousnesses may exist in every brain, rather like separate individuals. Consciousnesses are, by their nature, impossible to access. If we could examine their contents, they would be brought into the stream of ‘owned’ consciousness and so would no longer be separate. Only under certain extraordinary circumstances, such as split brain experiments and the ‘alien hand’ condition, do they come to light.
Points Of Consciousness
Some brain cells are responsible for producing an awareness of very specific things. Researchers used sensitive electrodes to record the activity of single neurons in the brains of monkeys. They identified one group of cells that became active only when a hand was passed from the right to the left of the animal’s visual field. The cells did not respond to the hand alone nor any other object moving on the same course. So, while consciousness emerges from the activity of the entire brain, some of its contents are due to very localized activity – right down to the level of single cells.
Seeing a grapefruit
When you notice an object like a grapefruit, specialized areas of neurons in your brain are stimulated in response to the color yellow, while others fire in response to the round shape. Together, they create your perception of the grapefruit.
Split Brains
The human brain has two cerebral hemispheres. The left hemisphere controls the right side of the body and contains the areas involved with language, while the right hemisphere controls the left side. However, research with ‘split-brain’ patients – where the connections between the hemispheres have been severed for medical reasons (usually the treatment of epilepsy) – has revealed more subtle differences between the hemispheres and led some psychologists to suggest that each hemisphere contains its separate consciousness.
In this research, the patient faces a screen with a picture on the left or right. The patient fixes their eyes on the center of the screen, and (because of the normal crossover in the visual pathways) the visual information enters the hemisphere opposite to the side on which the picture is presented. The normal connection between the hemispheres is severed, so the information stays ‘stuck’ in the receiving hemisphere.
The language centers are in the left hemisphere, so the patient can describe a picture only if the information enters the left hemisphere. If it enters the right hemisphere, the patient will claim to be unaware of the image. However, if asked to select an object matching the image by touching it with the left hand (which is controlled by the right hemisphere), the patient will often succeed. When asked why it is unconscious because it lacks verbal ability; in fact, it is capable of sophisticated cognition. One study bears out this conclusion. Researchers devised a way of ‘talking ‘exclusively to the right brain of a split-brain patient known as PS by giving his left hand. Scrabble letters to spell out messages from the right side of his brain. PS was asked what plans he had for his career. His spoken answer – that he intended to be a draughtsman – was provided by his left hemisphere(where the brain’s language capacity is primarily located ). In response to the same question, his right hemisphere gave a different answer, spelling out the words: ‘automobile drive.’ This newly revealed ambition could be the desire for separate consciousness in the right hemisphere – which, in normal circumstances, was unknown even to the boy himself.
