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Physiology of memory and emotions
& the limbic system
Prof. Vajira WeerasingheDept of Physiology, Faculty of Medicine,
University of Peradeniya
Terminology
• Cognition
• Memory
• Learning
• Speech and communication
• Emotions
• etc
Cognition
– the mental process of knowing, including aspects such as
• awareness • perception • reasoning • language • memory• Judgment
Emotions • a conscious mental reaction (as anger or fear)
subjectively experienced as strong feeling
usually directed toward a specific object
and typically accompanied by physiological
and behavioral changes in the body
– eg. happinessangerloveconfidenceanxietystressrelaxed
Physiology of memory
Answer following questions?
• Did you drink tea at breakfast?
• Can a rabbit play golf?
• Who sang the song “This land belongs to you”
• What South American country begins with S?
• How many eggs are in a dozen?
• What is Julius Caesar’s telephone number?
• Is welderly an English word?
• Do all birds fly?
memory
• highly organised
• there are ways to effectively and efficiently analyse, manipulate, search memory
• Process of storing and retrieving information in the brain
• This process is central to learning and thinking
memory
memorymemory process
• registration: transferring of information in to a form that can be retained
memorymemory process
• retention: storage of information
memorymemory process
• remembering: retrieval of information
memorymemory process
registration, retention, remembering
memory
There are four different types of remembering:
• recollection• recall• recognition• relearning
memoryThere are four different types of remembering:
• recollection: the reconstruction of events or facts on the basis of partial cues
• recall: the active and unaided remembering of something from the past
• recognition: the ability to identify previously encountered information as familiar
• relearning: the ability to learn once familiar material more easily than unfamiliar material
memory systems
• sensory memory orimmediate memory
• short term memorySTM or working memory
• long term memoryLTM
sensory memory or immediate memory
• lasting few sec (less than 2 sec)• act as buffers for stimuli received through senses• if ignored -> forgotten• If attention is paid -> passed into STM• visual sensory memory is more commonly referred to
as iconic memory • auditory sensory memory is known as echoic memory
short term memory• Known as primary, working or active memory• Stores a limited amount of information for about 30
sec • Contain recently processed sensory input or items
recently retrieved from LTM • With rehearsal can be kept for several min• acts as a scratch-pad for temporary recall of the
information • Has a limited capacity. Capacity is about 7 items ± 2
(memory span) • By chunking can remember more items (eg. phone
numbers)
Working memory• Structures and processes used for temporarily storing
and manipulating information• Is a workbench of mental processing• Composed two components
– Processes information in acoustic form– Visuospatial scratch pad
• Frontal cortex, parietal cortex, anterior cingulate, and parts of the basal ganglia are crucial for functioning
• (previously known as STM)
long term memory
• lasting days, months, yrs• Long-term memory can store a very large quantity of
information and • can maintain that information for very long periods of time• It holds many different kinds of information including:
– facts, events, motor and perceptual skills, knowledge of physical laws,
– spatial models of familiar environments,– attitudes and beliefs about ourselves and others
• Long term potentiation moves STM to LTM
STM
LTM
UnconsolidatedMemoriesDiscarded
Consolidation
Water tank model
Atkinson & Schiffrin (1968) Multistore Model of Memory
Sensory
Memory
LTM
STMStimuli
Attention
Transfer
Retrieval
Rehearsal
F O R G O T T E N
forgetting
forgetting• Is memory permanent?
• memory is known to decay with time
• disuse: regular retrieval enhances memory
• interference: new information interferes with old information or vice versa
• inaccessibility: tip of the tongue phenomenon
This example is based on memorizing that occurs during a one-hour lecture.
Further types of memory
• Explicit memory
• Implicit memory
– memories from events that have occurred in the external world
– facts and events– if the process of remembering involves the
conscious recollection of previous experiences
Explicit Memory
• Episodic memory» refers to memory related to specific events and experiences
in our life» eg. first time a dog bites you» Hippocampus and cortical areas may be involved
• Semantic memory» refers to memory related to general or generic knowledge» meaning of all words, symbols, rules, facts not tied to specific
events» eg. a child after seeing several dogs develop the concept of
“dog”» Hippocampus or widespread throughout the brain
Types of Explicit Memory
– Consist of memories necessary to perform events and tasks, or to produce a specific type of response
– if the process of remembering does not involves the conscious recollection of previous experiences
– Implicit memory is best demonstrated when performance is improved on a task
Implicit Memory
• Procedural memory• refers to memory related to knowledge concerning
learning that is obtained incrementally and that is inaccessible to conscious recollection
• learning how to perform a task or acquire a new skill• Motor cortical areas and cerebellum, basal ganglia may
be involved
• Priming• when subjects are exposed to a set of words and then
later tested it is said to be primed and recall is easier
Types of Implicit memory
Prospective memory• ability to plan and remember to perform future tasks• factors influencing
– cues, reminders, compliance, motivation, commitment
• Prospective memory can be further broken down into– Event-based prospective memory
» triggered by cues, such as remembering to post a letter (action) after seeing a mailbox (cue).
– Time-based prospective memory» triggered by a time-cue, such as going to the doctor (action)
at 4pm (cue).
• frontal lobe, prefrontal region and parietal cortex may play a role
• is called “remembering to remember”
Emotional memory
• memory for events that evoke a particularly strong emotion
• consciously available, but elicit a powerful, unconscious physiological reaction
• Involves amygdala
Learning Experiments• Ivan Pavlov has done experiment on Classical
Conditioning• Conditioned reflex using dog and salivation
Unconditioned stimulus: foodConditioned stimulus: BellResponse: Salivation
Neurolab
Operant Conditioning• B.F.Skinner (1904-1990) has done experiments on Operant
conditioning• These experiments were done using a Skinner's box
•This box is equipped with a lever when pressed releases a food pellet into a cup
•When a rat is put into this box initially by chance it will find that pressing the lever a food pellet is released.
•After that rat makes up a mental association between pressing the lever and release of the food.
•Rat now has a means of operating on the environment in a manner which is rewarding.
•Skinner called this rat's behavior: operant behavior
Synaptic strengthening
• Conditioning of synaptic activity
• Hebb first theorised this
• "cells that fire together, wire together"
• any two cells or systems of cells that are repeatedly active at the same time will tend to become 'associated', so that activity in one facilitates activity in the other
•Initially firing of AX neuron is active
•Firing of BX is inactive
A
B
X
•After conditioningcontinuous firing of A & B together
•Firing of BX becomes active
Habituation and sensitisation
• habituation – decrease in response with repetitive stimulation
• sensitisation – increase in response with repetitive stimulation
– These have been studied using gill withdrawal in Sea Snail Aplysia when the gill is stroked
– After a few strokes if the stimulus is harmless there is no withdrawal: animal get habituated
– If the stimulus is noxious then animal produces a more powerful withdrawal: sensitised
– neurotransmitters that play particularly important role in habituation are serotonin, acetylcholine, dopamine and glutamate
• LTP is a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously
• It is also defined as a persistent increase in synaptic strength following high-frequency stimulation of a chemical synapse
• LTP is widely considered one of the major cellular mechanisms that underlies learning and memory particularly long term memory
• LTP is known to occur in hippocampus
• LTP is known to be mediated by Ca influx in glutamate receptors
LTP (Long Term Potentiation)
LTP mechanism• Stimulation of presynaptic neuron• Release of glutamate• Binds to
– AMPA receptor• Na infux• EPSP is created
– NMDA receptor • Glutamate binds and open the ion gate• EPSP will remove Mg2+ which blocks the NMDA receptor • Result is Ca2+ influx
– Second messenger system
– Upregulation of AMPA receptors
– Release of retrograde paracrine substances (eg. NO)
• Long lasting EPSP
LTP significance
• Long term memory
• Plasticity (synaptic or cortical)– the changing of neurons, the organization of their
networks, and their function via new experiences
• Depression
• Parkinson's disease
• Epilepsy
• Neuropathic pain
• Alzheimer's disease
• Drug addiction
NMDA receptor– n Methyl d Aspartate receptor has a role in the
memory processes occurring in hippocampal neurons
– NMDA receptor is both voltage gated and ligand gated
– NMDA receptor activity causes Ca2+ influx which is an important mechanism of LTP
NMDA receptor modulators
• Glutamate or aspartate (less effective) binds
• Glycine biding is also necessary
• Mg2+ blocks
• Membrane depolarisation
• Antagonists– Anaesthetics, alcohol, ketamine
• limbic system (hippocampus, amygdala)
• thalamus• frontal lobe• interconnections
brain areas responsible for memory
History• 1980s: James and Lange developed a theory of emotion stating
that emotional experience was nothing more than conscious awareness of autonomic activity in the body
• 1920s: Cannon and Bard proposed an alternative theory of emotion which held that portions of the brain, the hypothalamus and thalamus,mediated emotion
• 1937: Papez proposed that the limbic system, a ring of primitive cortex was the critical brain system mediating emotion
• 20th century: Papez’s conception of the limbic system was expanded to include a number of additional brain areas which are interconnected with the ring of primitive cortex, eg. amygdala
Papez circuit
A long circuitous conduction chain in the mammalian forebrain, leading from the hippocampus by way of the fornix to the mammillary body and thence returning to the hippocampus by way of, sequentially, the anterior thalamic nuclei, cingulate gyrus, and parahippocampal gyrus
limbic system
• nuclei– amygdala– septal nuclei– mammillary body– hypothalamus
• cortical areas– hippocampal gyrus– cingulate gyrus– dentate gyrus– entorhinal, amygdaloid cortex
• paralimbic structures• orbital gyrus, insula, nucelus accumbens, thalamic nuclei, superior
temporal gyrus,
• fibre tracts: fornix, medial forebrain bundle
limbic cortex
• consist of 3 layered cortex (in contrast to 6 layered cortex of the neocortex)
• Limbic system is a link between the brain stem and neocortex
• Limbic structures are connected to each other and with the association cortex and the brain stem
• Medial forebrain bundle is a major efferent connection of the limbic system:
• projected to the hypothalamus, reticular formation. Influence on autonomic and endocrine activity
• Amygdala receives inputs from olfactory pathways
• Connections with the neocortex provide a synthesis of emotional and rational thought
FunctionsLimbic system is also referred to as the
‘emotional brain’
• Emotional (include motor activity)• Behavioural (Motivations, Drives: appetite,
thirst, sexual behaviour, Reward system)• Memory
– Utilizes the hypothalamus to effect the physical manifestations associated with emotions, etc.
Complex role of the limbic system
• as an intermediary between– external events (carried to the CNS via afferents)– our processing of those events (involving cortical
and subcortical brain areas) – our responses to those events (both behavioral and
autonomic)
Role in memory storage
• Working memory—short term – cortical phenomenon
• Explicit (declarative)—factual knowledge– temporal events, stored in hippocampus
• Examples: what innervates biceps femoris m.?
• Implicit (procedural)—learned skills– unconsciously recalled—includes emotional
responses—stored in amygdala (at least in part)• Examples: writing, playing a musical instrument
Hippocampus• is a part of the brain located
inside the temporal lobe• plays a major role memory
consolidation • responsible for spatial memory• might act as a cognitive map —
a neural representation of the layout of the environment.
• In Alzheimer's disease, the hippocampus becomes one of the first regions of the brain to suffer damage
Physiology of emotions
Physiology of emotions
• Within the limbic system, emotional impulses originate in the amygdala
• A network of neural pathways connect the amygdala to the neocortex, the "thinking brain," allowing us to reflect on our feelings and to think before acting
• In times of perceived crisis, however, those pathways are bypassed and impulse overrides reason and the amygdala takes over the brain
Physiology of emotions • Each emotion sparks a distinctive physiological
reaction
• Happiness cues the brain to suppress worrisome or negative feelings and increases the body’s energy level
• Sadness does the opposite, slowing down its metabolism
• Anger floods the brain with catecholamines
• *Stress and *anxiety set off the nervous system’s "flight-or-fight" response
Neurotransmitters released
• Ach
• Dopamine
• Endorphines
• GABA
• Glutamate
• Norepinephrine
• Serotonin
Limbic system
• Amygdala– Involved in aggression, jealousy, and fear;
• Cingulate gyrus– Autonomic functions regulating heart rate and blood
pressure as well as cognitive and attentional processing; • Fornicate gyrus
– Region encompassing the cingulate , hippocampus , and parahippocampal gyrus;
• Hippocampus– Required for the formation of long-term memories;
• Hypothalamus– Regulates the autonomic nervous system via hormone
production and release. Affects and regulates blood pressure, heart rate, hunger, thirst, sexual arousal, and the sleep/wake cycle;
Limbic system
• Mammillary body– Important for the formation of memory;
• Nucleus accumbens– Involved in reward, pleasure, and addiction;
• Orbitofrontal cortex– Required for decision making;
• Parahippocampal gyrus– Plays a role in the formation of spatial memory.
• Septum– regulates emotion and the ability to learn and control
impulses as well as such drives as sex, hunger, thirst and aggression
Amygdala
• Is part of the limbic system
• located deep within the temporal lobes, medial to the hypothalamus and adjacent to the hippocampus
• Functions: – Arousal – Controls Autonomic Responses Associated with
Fear (“fear centre”)– Emotional Responses – Hormonal Secretions – Memory
Amygdala• As a central component of the limbic system,
the amygdala oversees emotional processing
• Its principal task is to filter and interpret sophisticated incoming sensory information in the context of our survival and emotional needs, and then help initiate the appropriate responses.
– In a recent imaging study pictures of frightening faces initiate a quick rise and fall of activity in the amygdala
Prefrontal Cortex • The most frontal part of the frontal cortex
• Connected to reticular
• Performs executive functions
• Involved in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior
• Activity of this region is considered to be orchestration of thoughts and actions in accordance with internal goals
Nucleus accumbens
• It is part of the striatum
• It is known as the “pleasure centre”
• It is thought to play an important role in reward, pleasure, laughter, addiction, aggression, fear, and the placebo effect
• GABA is present
• Output to globus pallidus, limbic system, reticular formation
Executive functions
• Executive functions relate to – abilities to differentiate among conflicting thoughts– determine good and bad, better and best, same and
different– future consequences of current activities– working toward a defined goal– prediction of outcomes– expectation based on actions– social "control" (the ability to suppress urges that, if
not suppressed, could lead to socially-unacceptable outcomes)
