Consciousness, Thought, and Memory Cristina Krage, Anthony Kurland, and Malynda Clark

What is Consciousness? Consciousness is a difficult concept to define. Even today, not everything regarding its complexities is fully understood. However, we do know that it is graded on a continuum, ranging from alertness at the highest state, through drowsiness/lethargy, stupor, and coma at the lowest state. It involves the voluntary initiation and control of movement, the perception of sensation, and higher mental processing (memory, logic, judgment, etc). To be functional, simultaneous stimulation of large areas of the cerebral cortex must occur. This activity is superimposed on other types of neuronal activity. This activity can be both regional and/or involved in cognition. In any case, the idea of consciousness is holistic and totally interconnected within the cerebrum.

What is Memory? Memory is the storage and retrieval of information. The two stages of memory are short term (STM) and long term (LTM). STM is the first step, and is limited to seven or eight chunks of information. Some 5% of sensory input is transferred to the STM. The LTM is of limitless capacity, but its ability to store and retrieve information declines with aging. The transfer of information from STM to LTM is affected by emotional state, rehearsal (repetition), association (tying new information to old), and automatic memory (memory that is not consciously formed). The consolidation of memory involves fitting new facts into various categories of knowledge already stored in the cerebral cortex. These newly stored memories are usually filed along with the context in which they were learned.

Categories of Memory Declarative (fact) memory- learning specific information (names, faces, words, and dates) related to conscious thought and the ability to manipulate symbols and language. Nondeclarative memory- less conscious or unconscious learning. This type of memory contains 3 subcategories: procedural (skills) memory, motor memory, and emotional memory. These are acquired through experience and repetition, and do not preserve the circumstance of learning.

Brain Structures involved in Memory Specific pieces of memory are stored near regions of the brain that need them. Pathway of Memory Storage: Association cortices -> medial temporal lobe (hippocampus and temporal cortical areas) -> thalmus and prefrontal cortex <-basal forebrain Memories are retrieved when the same sets of neurons that were initially involved in memory formation are stimulated.

Mechanisms of Memory During learning: 1. Neuronal RNA content is altered and newly synthesized mRNAs are delivered to axons and dendrites 2. Dendritic spines change shape. 3. Unique extracellular proteins are depositited at synapses involved in LTM 4. The number and size of pre-synaptic terminals may increase 5. More neurotransmitters are released by pre-synaptic neurons.

Alzheimer’s Disease In this disease, normal storage and retrieval of memory is disrupted by plaques, which accumulates between neurons, and tangles, twisted sections of the protein tau (which normally supports neuronal structure), causing cell damage and death. People afflicted with this disease present all the symptoms one would expect from a disorder of its nature; forgetfulness, personality changes, poor judgment, etc. These symptoms demonstrate the complexity of the nervous system, particularly the cerebrum as it pertains to consciousness and memory. If the slightest element should become ineffective, the entire system often follows soon after.

Thought The phenomena of thought has been puzzled over by philosophers, scientists, and other men of great learning for thousands of years. Despite the great advances we have made in technology and available data, exactly how and why we think is mostly still a mystery. However, it is often equated to awareness of the subconscious, which encompasses all actions performed without the conscious decision to do so, and conscious mind.

Sources Human Anatomy and Physiology, Seventh Edition. Marieb, Elaine N. and Hoehn, Katja. 2007. Pukamble.tripod.com MayoClinic.com