1. PhD MD MBBS Faculty of Medicine Al Maarefa Colleges of Science & Technology Faculty of Medicine Al Maarefa Colleges of Science & Technology Lecture – 13: Memory Nervous System Physiology By Dr. SHAHAB SHAIKH PhD MD MBBS Faculty of Medicine Al Maarefa Colleges of Science & Technology Faculty of Medicine Al Maarefa Colleges of Science & Technology

2. HIGHER FUNCTIONS OF BRAIN –LEARNING –MEMORY –JUDGEMENT –LANGUAGE –SPEECH 2

3. MEMORY Memory is the process in which information is encoded, stored, and retrieved. Learning and memory are attributed to changes in neuronal synapses, thought to be mediated by long-term potentiation and long-term depression. Stages in the formation and retrieval of memory: Encoding: –receiving, processing and combining of received information Storage: –creation of a permanent record of the encoded information Retrieval: –calling back the stored information in response to some cue for use in a process or activity 3

4. MEMORY Memories are stored in the brain at synapses by changing the basic sensitivity of synaptic transmission between neurons. The neural change at synapses which is responsible for retention or storage of knowledge is known as memory trace. Once memory trace are established, they can be activated by thinking mind to reproduce memory. Memory traces occur at many regions of brain at cortical and subcortical regions. Important areas associated with memory are: cerebral cortex (motor, sensory, visual & auditory) prefrontal cortex hippocampus & medial temporal lobe Amygdala limbic system thalamus cerebellum 4

5. MEMORY The hippocampus, the amygdala, the striatum, or the mammillary bodies are thought to be involved in specific types of memory. Hippocampus is believed to be involved in spatial learning and declarative learning, while the amygdala is thought to be involved in emotional memory. 5

6. MEMORY - TYPES 6

7. MEMORY - STAGES 7 Sensory 1.Large capacity 2.Contains sensory information 3.Very brief retention (1/2 sec for visual; 2 secs for auditory) Sensory 1.Large capacity 2.Contains sensory information 3.Very brief retention (1/2 sec for visual; 2 secs for auditory) Short Term 1.Limited capacity 2.Brief storage (up to 30 seconds w/o rehersal) 3.Conscious processing of information Short Term 1.Limited capacity 2.Brief storage (up to 30 seconds w/o rehersal) 3.Conscious processing of information Long Term 1.Unlimited capacity 2.Storage presumed permanent 3.Information highly organized Long Term 1.Unlimited capacity 2.Storage presumed permanent 3.Information highly organized

8. 8 MEMORY - STAGES

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10. MEMORY - TYPES 10 Declarative (Explicit) memory: Memory of factual knowledge & personal experiences Semantic Memory: Impersonal facts and everyday knowledge Episodic Memory: Personal experiences linked with specific times and places Procedural (Implicit) Memory: Long-term memories of conditioned responses and learned skills, e.g., driving

11. LONG TERM MEMORY 11 long-term memory is generally believed to result from actual structural changes, instead of only chemical changes, at the synapses and these enhance or suppress signal conduction. The most important of the physical structural changes that occur are the following: 1.Increase in vesicle release sites for secretion of transmitter substance 2.Increase in number of transmitter vesicles released 3.Increase in number of presynaptic terminals 4.Changes in structures of the dendritic spines that permit transmission of stronger signals Thus, in several different ways, the structural capability of synapses to transmit signals appears to increase during establishment of true long-term memory traces.

12. MEMORY - TYPES Positive and Negative Memory-"Sensitization" or "Habituation" of Synaptic Transmission: Although we often think of memories as being positive recollections of previous thoughts or experiences, probably the greater share of our memories is negative, not positive. Brain has the capability to learn to ignore information that is of no consequence. This results from inhibition of the synaptic pathways for this type of information; the resulting effect is called habituation. This is a type of negative memory. Conversely, for incoming information that causes important consequences such as pain or pleasure, the brain has a different automatic capability of enhancing and storing the memory traces. This is positive memory. It results from facilitation of the synaptic pathways, and the process is called memory sensitization. 12

13. MEMORY - TYPES 13

14. MEMORY - TYPES 14

15. MEMORY - FORMATION MEMORY INVOLVES –RECEPTION OF INFORMATION –FORMATION OF MEMORY TRACE –CONSOLIDATION OF MEMORY TRACE BY REHERSAL –RECALL OF MEMORY TRACE 15

16. MEMORY - FORMATION Consolidation of memory: For short term memory to be converted into long term memory it must be consolidated Consolidation occurs by repeatedly activating the short term memory, which will initiate chemical, physical and anatomical change in the synapses that are responsible for long term memory It takes 5 to 10 minutes for minimal consolidation and one hour or more for strong consolidation factors which prevent consolidation: –Head injury – brain concussion –Deep general anesthesia –Electrically induced brain convulsions 16

17. MEMORY – IMP. REGIONS IN BRAIN Short Term Memory – Hippocampus, Medial Temporal Lobe Long Term Memory – Neocortex Declarative Or Explicit Memory – Hippocampus Skill Or Implicit Memory – Cerebellum, Basal Ganglia. Working Memory – Prefrontal Cortex Memories Visual, Olfactory, Auditory Are Located In Respective Cortical Regions. 17

18. LOSS OF MEMORY Loss of Memory is called Amnesia. Hippocampus removal (for temporal lobe epilepsy) or lesion – mainly anterograde amnesia, little retrograde. Thalamic lesion mainly retrograde amnesia PAST PRESENT INCIDENT Retrograde Amnesia Anterograde Amnesia

19. LOSS OF MEMORY Anterograde amnesia: –the inability to form new explicit long-term memories for events following brain trauma or surgery. –Explicit memories formed before are left intact. – Cause possibly is damage to hippocampus Retrograde amnesia: –the disruption of memory for the past, especially episodic memory. –After brain trauma or surgery, there often is retrograde amnesia for events occurring just before. Infantile/child amnesia: –the inability as adults to remember events that occurred in our lives before about 3 years of age. –Due possibly to fact that hippocampus is not fully developed.

20. LOSS OF MEMORY When retrograde amnesia occurs, the degree of amnesia for recent events is likely to be much greater than for events of the distant past. The reason for this difference is probably that the distant memories have been rehearsed so many times that the memory traces are deeply ingrained, and elements of these memories are stored in widespread areas of the brain. In some people who have hippocampal lesions, some degree of retrograde amnesia occurs along with anterograde amnesia. Damage in some thalamic areas may lead specifically to retrograde amnesia without causing significant anterograde amnesia.

21. DEMENTIA Impairment of memory, intelligence and personality without impairment of consciousness. 21

22. References Human physiology by Lauralee Sherwood, 8 th edition Text Book Of Physiology by Guyton & Hall, 11 th edition

23. 23 THANK YOU

24. A thought for the day... A thought results from a "pattern" of stimulation of many parts of the nervous system at the same time, probably involving most importantly the cerebral cortex, thalamus, limbic system, and upper reticular formation of the brain stem. The stimulated areas of the limbic system, thalamus, and reticular formation are believed to determine the general nature of the thought, giving it such qualities as pleasure, displeasure, pain, comfort, crude modalities of sensation, localization to gross areas of the body, and other general characteristics.

25. A thought for the day... Consciousness can perhaps be described as our continuing stream of awareness of either our surroundings or our sequential thoughts.