Learning And Memory

Learning and Memory

• Learning and memory form the principal higher intellectual functions. • Learning is defined as the process by which new information is acquired. It is the process by which behavior is altered by experience. • There is an intricate relationship between learning and memory in that memory is the ability to recall learnt information. • There are basically two types of learning: Associative and Non-associative learning

• Associative learning: involves learning about relations between two or more stimuli simultaneously. For example the conditioned reflex • Non-associative learning: involves response to only one type of stimulus based on factors like habituation and sensitization. Habituation: this means getting used to a constantly exposed stimuli. During the first experience, the stimulus is novel evoking a response, however with repeated exposure, response becomes progressively reduced until the individual is habituated. Sensitization: this simply means amplification of response to stimuli i.e a state in which the body becomes more sensitive to a stimulus. If a stimulus to which an individual is habituated is combined with another stimulus (pleasant or unpleasant) the individual becomes more sensitive to the original stimulus. E.g A woman who is used to sleeping with noise will suddenly wake up when her baby cries

Memory

• Memory is defined as the ability to recall the past experience learnt. • Memories are stored in the brain by changing the basic sensitivity of synaptic transmission between neurons as a result of previous neural activity. The new or facilitated pathways are called memory traces. They are important because once the traces are established, they can be selectively activated by the thinking mind to reproduce the memories. • POSITIVE and NEGATIVE MEMORY • Although we often think of memories as being positive recollections of previous thoughts or experiences but it seems the greater share of our memories is negative, not positive. • But if our minds attempt to remember all information from our senses the memory capacity of the brain would be overwhelmed. Fortunately, the brain has the capacity to learn to ignore inconsequential information. This results from inhibition of the synaptic pathways for this type of information resulting in memory habituation. This is a type of negative memory

• Conversely consequential information such as pain or pleasure lead to an enhanced storage of memory traces. This is a type of positive memory. It results from facilitation of the synaptic pathways, and the process is called memory sensitization • CLASSIFICATION OF MEMORIES • There are various degrees of memory, some remain only for few seconds while others last for hours, days, months or years • Implicit memory: aka non declarative memory or skilled memory. Here past experiences are utilized without conscious awareness. It is necessary for skilled activities like cycling, driving, typing etc • Explicit memory: aka declarative memory. It is memory that involves conscious recollection of past experience. It involves recalling external events occurring around us

• Memory can also be classified as Short term; intermediate long term and long term • Short term memory: • It is recalling events that happened very recently i.e within hours or days • this is theoretically believed to be caused by continual neural activity resulting from nerve signals that travel around and around a temporary memory trace in a circuit of reverberating neurons. • Short term memory is typified by one’s memory of 7 to 10 numerals in a telephone number for a few seconds to a few minutes at a time but lasting only as long as the person continues to think about the number or facts • It can be interrupted by stress, trauma and drug abuse

• Intermediate long term memory: this memories may last for many minutes or weeks. They can be lost unless the memory traces are activated enough to become more permanent. • The molecular mechanism for this type of memory are the: Mechanisms for facilitation: It is believed to be due to stimulation of facilitator presynaptic terminal and sensory terminal with release of serotonin at the facilitator synapse onto the surface of the sensory terminal Serotonin acts on serotonin receptors in the sensory terminal memb, these receptors activate adenyl cyclase. This enzyme cause formation of cAMP cAMP activates protein kinase that cause phosphorylation of a potassium channels in the sensory terminal, this in turn blocks the potassium conductance. This blockage last for minutes up to several weeks

The lack of potassium conductance causes a greatly prolonged action Potential The prolonged AP causes prolonged activation of calcium channel allowing large influx of calcium ion in the sensory synaptic terminal, this cause greatly increased NT release to the subsequent neuron. Mechanism for habituation: the habituation effect in the sensory terminal results from progressive closure of calcium channels through the terminal membrane. • Long term memory: it is believed that the development of true longterm memory depends on physically restructuring the synapses themselves in a way that changes their sensitivity for transmitting nervous signals the most important of these changes are: Increase in vesicle release sites for secretion of NT Increase in number of transmitter vesicles released Increase in no. of presynaptic terminals Changes in structure of the dendritic spines that permit stronger transmission of stronger signals Long term memory is also called remote memory and it is involved in recalling of the events of weeks, months, years or even a lifetime.

• Longterm M is more resistant and is not easily disrupted • Based on duration it can be • Sensory memory:this is ability to retain sensory signals in the sensory areas of the brain. this is retained only for a short period. It is the initial stage of memory. They are easily replaced. • Primary memory: this is the memory of facts, words, numbers, letter or information recalled for few secs to minutes. E.g recalling a phone no.. It is esay to recall but easily repaced by new memory e.g looking up another phone no. • Secondary memory:this is storage of info in the brain for a longer period.

CONSOLIDATION OF MEMORY

• Process by which short term memory is crystallized into long term memory. It causes permanent facilitation of synapse. • It is possible by rehearsal mechanism i.e rehearsal of the same info again and again accelerates and potentiates the degree of transfer of short term memory to long term. • APPLIED PHYSIOLOGY • Amnesia: • Retrograde (failure to recall past remote long term memory due to temporal lobe syndrome) and Anterograde (failure to establish new long term memory due to hippocampal lesion) • Dementia • Drugs Faciltating Memory • Caffeine, amphetamine, nicotine