Amnesia and Biological Bases of Memory
Key Terms from Lecture
Engram – memory record.
Plasticity – the ability of neurons and the brain to change in response to experience.
Long-term neural plasticity – changes in the structure of neurons as a result of experience.
Immediate neural plasticity – changes in neuronal function as a result of experience.
Cell assemblies – networks of cells firing together.
Long-term potentiation (LTP) – the process by which cell assemblies, or networks of neurons,
become more responsive following synchronized firing that is consistent over time. According
to Hebb, restimulating any neuron in the network will increase the firing rate of the whole
Habituation paradigm – a method used to study the immediate changes that occur in neuronal
function as a result of experience. Immediate changes are mediated through a decrease in
release of a neurotransmitter. In other words, there is a decrease in responding to repetitive
Sensitization paradigm – a method used to study the immediate changes that occur in neuronal
function as a result of experience. Immediate changes are mediated through an increase in
release of a neurotransmitter. In other words, there is an increase in responding to repetitive
Limbic system – brain structures involved in emotional processing and memory processing.
Includes hippocampus, amygdala, fornix, frontal lobes, and thalamus.
Papez circuit – an interconnected loop of brain structures originally thought to be the neural
basis for emotional experience. It was later determined to be critical for both emotion and
Post-traumatic amnesia – loss of memory for information from the onset of head trauma until
continuous memory is restored.
Retrograde amnesia – loss of memory prior to head trauma.
Anterograde amnesia – the inability to learn new information.
Hippocampus – brain structure in the medial temporal lobe shown to be important for memory
consolidation via LTP. It is one of the structures of the limbic system and part of Papez circuit.
Page 1 of 5 Hippocampal amnesia – also known as the “classic amnesia.” This type of amnesia results
from damage to the hippocampus. Damage may be due to infections (e.g., encephalitis), disease
states (e.g., epilepsy), surgery (e.g., to relieve intractable seizures), stroke, etc. Deficits are
primarily in episodic memories.
Thalamus – structure deep inside the center of the brain also shown to be important for retrieval
of memories. It is one of the structures of the limbic system and part of Papez circuit.
Thalamic amnesia – amnesia due to damage to the thalamus such as stroke or injury. Deficits
may be primarily in retrieval of information or in autobiographical memory.
Amygdala – structure located in front of the hippocampi shown to be involved in emotional
functioning, particularly fear/anxiety and conditioned learning. It is one of the structures of the
Item memory – memory for the informational content of an event.
Source memory – memory for the origin of information, contextual details of an event.
Key Concepts from Lecture
1. How is memory stored in the brain by neurons?
a. Mechanisms for learning must have the following properties:
i. Very fast
ii. Long lasting
iii. Relatively consistent
b. Plasticity – the ability of neurons and the brain to change in response to
i. Long-term – structural changes in neurons.
1. Cell complexity
ii. Immediate – functional changes in neurons.
1. Very fast changes in neurons mediated by increases or decreases in
neurotransmitter. Examples include the habituation and sensitization
responses of Aplysia.
c. Long-term potentiation (LTP) according to Hebb:
i. Networks of neurons that consistently fire together at the same time become
ii. Potentiation refers to the facilitation in restimulating the network’s
response/firing rate. It is important to note that restimulating any of the
individual neurons in the network results in an increase in the whole network’s
iii. In other words, “neurons that fire together wire together” and “code” a single
iv. Hebb believed that LTP may have been the basis for complex learning.
Page 2 of 5 2. Learning and retrieval of memories
a. Hebb’s two stages of memory formation
i. Short-term memory (STM)
1. The “activated” information is available in consciousness.
2. As long as the cell assembly continues reverberating, the information
is available in STM. Reverberation is analogous to rehearsal in STM,
but at the cell assembly level.
ii. Long-term memory (LTM)
1. If reverberations occur over a long enough period, structural changes
in the anatomy of the neurons occur.
a. Examples of structural changes include the following:
i. Increase in number of receptors, which helps strengthen
ii. Increase in production and release of neurotransmitters.