Sunday, July 1, 2007

Threads of consciousness

As the study of the mind continues to explore the labyrinth that is consciousness, fleeting images of its essence are beginning to slowly reveal it’s mysteries to us. Though the tools available for probing this elusive quality are still primitive and limited, they are providing glimpses of how the layered interactions between innumerable regions of the brain merge to produce manifestations of what we describe as conscious thought.

In broad terms, the blended layers of our brains create a fluid stream of sensory input that flows from the brainstem and mid-brain regions, spreading up throughout the limbic system and cortex. The sensory input is received through the variety of senses and is streamed along two main paths; one directed towards the limbic system, and the other to the thalamus.

The limbic region process “good or bad” reactions to the input and eventually interacts with subsequent regions of the brain that have reacted or refined other streams of input. The thalamus relays sensory input outwards in parallel paths to other brain regions specialized to process specific types of information (auditory, tactile…). These regions are packed with specific types of neurons that lie in broad regions that are comprised of sub-regions that further articulate the type of information as in vision for example, where color, motion, and form are detailed. Further, deeper into these layers there are other sub-regions that detect extremely specific inputs, such as a specific color type.

The general flow of information bits are received by other regions that are sensitive not to sensory stimuli but to combinations of these stimuli. For example, they might combine and odor and location. The general concept is that these regions begin to formulate aggregates or packages of information in increasingly complex fashion.

As this information proceeds through the cortex it is combined with regions that maintain “records” of past experiences and are integrated into “action schema” that basically ready the brain to respond physically if events so demand.

This total package represents a reflection of data from the outside world combined with this brains personal nuanced experiences, memories, and associations. This information is not a perfect reception and as Rita Carter (Exploring Consciousness) describes it is “…like information traveling along a bad telephone line, it has been subject to various errors and distortions.”

Before become a response, or a conscious thought, these stimuli are further analyzed in area such as the frontal cortex where the ‘action schemas” and the responses they ready are inhibited until these regions tumble these packages around mixing these fully formed perceptions with further “working memories” readying as Carter notes “rational response to what is going on.”

This active dance of complex events provides the glimmerings of what is described as the phenomena of consciousness. The following is a list of some of the brain regions that seem to play a role in the mysterious development of human consciousness that neuroscience is slowly unraveling.

Thalamus: Directs attention and switches sensory input on and off.

Reticular formation: Activity here stimulates the cortex into action-without which there is no consciousness.
Hippocampus: Personal memories are coded here and it is also responsible for spatial memory (in the right hemisphere) - two linchpins of consciousness.

Parietal/Temporal junction:This is where the brain stores its “map” of self and judges the self’s relationship to the world. Has good connections to the frontal lobes and is in a position to pull in information from sensory areas. The “locus” of consciousness?
Temporal lobe: Store personal memories, processes sound and speech. Language may be the scaffolding that supports consciousness.
Left hemisphere: The dominant side in 97% of people, and usually the only one to use language. Its ability to describe experience, and spin stories, may be the means by which we become fully conscious.

Orbitofrontal cortex: Emotion becomes conscious here. If it’s not active, emotion is reduced to a robotic reflex without feeling.
Dorsolateral prefrontal cortex/ working memory: Where different ideas and perceptions are brought together. Could consciousness depend on this type of “binding”?
Motor cortex: consciousness dependant on body awareness? If so, the motor cortex must be of central importance.
Primary visual cortex (V1): Take this away and you lose visual consciousness even if other vision-processing areas are preserved.
Supplementary motor cortex (sma): This is where actions are “rehearsed”. Was this the brain function that jacked us up to consciousness?”

Daniel Dennet puts it aptly: “You enter the brain through the eye, march up the optic nerve, round and round the cortex looking behind every neuron, and then, before you know it, you emerge into daylight on the spike of a motor nerve impulse, scratching your head and wondering where the self is.”

Ref: Carter, R. Exploring consciousness.Univ of California Press. Berkeley,California.2002

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