CSB332 Lecture 13
- Some psychiatric disorders or mental dysfunctions occur because of abnormal changes in the
synaptic structure of the nervous system. Most of the time, these changes are abnormally
introduced and are beyond our control. They may be a product of neurotoxins from the
environment or part of traumatic experiences that impose pressure and demand on the nervous
- We can also introduce favourable changes within our nervous system, which is within our
control, through the process of learning. Learning introduces synaptic changes. We are able to
sculpt our brain and make it more adaptive in facing challenges in the environment.
- This model explains how information from the environment is stored in different stages with in
- Incoming information from many sensory modalities are first delivered to the first stage of
memory storage called sensory memory. Sensory memory is an imprint of environmental
stimuli that remain in the sensory receptors. Sensory memory provides an imprint of the
stimulus in the primary sensory cortices of the brain. If we don’t selectively attend to the
stimulus, then it will rapidly decay so that we eventually forget the stimuli.
- Sensory memory is information that is received by sensory receptors. Sensory memory has to be
attended to selectively. You have to be consciously aware of it before this information can get
stored in a longer term memory storage called short-term memory (STM) or working memory.
- STM information stays a little bit longer, but there are also limitations.
o The duration is not as long as you would want it to be. When you withdraw the stimulus
after 15 seconds, the stimuli will be forgotten if they are not properly encoded.
o STM can only store so much information, about 5-9 units or objects at the same time
from one stimulus. There are ways to increase the capacity of STM, such as chunking
information into meaningful units or using mnemonics.
- The information is registered by the sensory system, attended to, and eventually relayed to a
more complex structure in the brain which is the prefrontal cortex. This is where STM takes
place. When the information is in the prefrontal cortex, a lot of things can happen.
o STM can be conveyed for longer storage in different parts of the brain.
o The information that is in the prefrontal cortex can also access, spontaneously and
consciously, dormant or subconscious memories from other parts of the brain when
some information in STM stimulates or primes it.
Psychotherapists and clinical psychologists use STM to access many other parts
of the brain that contain dormant and subconscious information.
- Once the information is drawn in the STM, it is going to be forgotten unless you actively retain
that information in working memory through the process of rehearsal. You have to practice
imaging the stimulus in the prefrontal cortex, consciously analyze the information being
presented, sort out the information, actively associate the information with other information
stored in other parts of the brain, etc. until the information can get completely and efficiently
coded and transferred to a longer term memory storage located in other parts of the brain.
Once retained in LTM, which can either be episodic, semantic, or procedural memories, it can be
retained there for an infinite amount of time. - When you try to actively store information from STM to LTM, some features of the stimulus can
influence how you encode it. There are some stimuli that get more efficiently stored in LTM. The
ability to store information in LTM also depends on the intrinsic features or properties of the
- Depending on the type of information being received, it relays this information into different
parts of the brain for LTM storage or encoding. There are two general types of memory
- Explicit memory
o Memory information that you can readily formulate a proposition or declaration or
narration. This is information that you can transmit verbally to another person.
o Semantic memory
Memory about factual information.
o Episodic memory
Memory storage for personal events or experiences.
- Implicit memory
o Memory information that you can’t efficiently narrate to a person, but you can
demonstrate. Unconscious form of memory that you can’t transmit to another person,
but you can demonstrate it.
o Procedural memory
Memories of skills and habits.
o Non-associative learning
Ways of obtaining information from the environment via non-associative ways.
This is information that is reflexive or easily accessed without being conscious
about it or associating it with other things.
o Associative learning
Ways of obtaining or storing information by associating the information with
other information in the brain.
Stored information via associations that modify how you behave or
Stored information via associative learning for emotional responses.
- Learning induces structural changes in the brain.
- If there is a modification in the structure of the synapse, then there will also be modifications in
the function of the synapse. If a synapse becomes larger, then the signal that you can get from
neurons in the synapse will also get larger.
- Hebbian synaptic plasticity occurs when the presynaptic axon and the postsynaptic neuron are
activated almost simultaneously. The postsynaptic cell should also be activated at the same time
as the presynaptic axon. Slide 7
- Habituation and sensitization are very simple types of learned information (e.g., non-associative
- Sensitization is different and somewhat opposite from habituation.
- Aplysia is a marine snail. Researchers observed of reflexive behaviours in the Aplysia such as gill-
withdrawal reflex or siphon-withdrawal reflex. Researchers have determined the mechanism