Memory Lecture 21

Synesthesia

condition characterized by unusual blending of perceptions between different sensory modalities

Working Memory

• AKA short-terms memory

• Lasts seconds to a few minutes and can only hold so much

Long Term Memory

Memories that have been stored in a permanent manner

How can information enter long term memory?

Repetition

What type of information is more easily stored in long-term memory?

• Things that have more meaning or emotional salience

• Things that have a relation to material already known

What does long-term memory involve?

information storage and retrieval

What does storage involve in LTM?

structural change in the nervous system

Consolidation

a process in which new memories become more stable and robust with time

What does retreival involve in LTM?

mechanism of access to the stored memory

Why does forgetting something occur? What fails?

• Either storage or retrieval fails

• An event may be experienced and registered in WM but never retained in LTM

• Or once in LTM, the stored memory may be lost over time so there is less to retrieve

Amnesias

pathological memory problems

Retrograde Amnesia

• Inability to recall events before the onset of amnesia

• Memories of past experiences are either lost or unable to be retrieved from LTM

Anterograde Amnesia

• Inability to recall events after the onset of amnesia

• Experiences are not retained in LTM

• More of a problem when learning new information

What type of trauma is amnesia associated with?

Physical trauma to the brain:

• cellular damage from stroke or seizure

• brain tumor

• infection

• traumatic injury sustained from an accident

Electroconvulsive Shock Therapy (ECT)

• A psychiatric procedure in which seizures are induced in a patient to reduce symptoms of depression

• Produces retrograde amnesia because ECT disrupts memory consolidation so that recent memories are lost

Dementia

• A neurological condition characterized by global loss of cognitive abilities such as memory, attention, judgement, problem solving, planning, and motor coordination

• Memory problems begin with anterograde effects — the inability ot retain new information

• Severe dementia leads to retrograde memory loss

What are the two common forms of dimentia?

Vascular and Alzheimer’s

Vascular Dimentia

accumulation of cellular damage in the brain related to impaired blood circulation, generally due to strokes

Alzheimers Dementia

associated with senile plaques and neurofibrillary tangles being present in the brain, but its cause is ultimately unknown

Senile Plaques

extracellular deposits of aggregates of polypeptide called beta amyloid

Neurofibrillary Tangles

aggregates of tau protein involved in the assembly and stablization of microtubules

Sedative-hypnotics

drugs related to memory impairment during periods of use

Alcoholic “blackout”

• State of intoxication in which the drinker is awake, moving around, engaged in conversation, but then has no memory of the event the next day

• Information never made it into LTM

What is heavy alcohol consumption over extended periods of time associated with?

permanent memory impairment, a dementia, resulting from alcohol-related neurological damage

Benzodiazepines

frequently prescribed to treat anxiety or help with sleep, often causes memory impairment

Midazolam (Versed)

• A type of benzodiazepine given during medical procedures where the patient is only partially anesthetized

• Anterograde amnesic properties of midazolam impair the person’s ability to remember uncomfortable parts of the procedure

Nonbenzodiazepine Hypnotics

• Often prescribed for insomnia that produces anterograde amnesia

• Reports of people engaging in strange or dangerous behaviors with no memory of doing so

What does regularly ingesting multiple prescribed medications lead to amongst the elderly?

memory impairment and mental confusion

Nootropic

drugs that improve effects on aspects of cognition, incloding memory

Karl Lashley

• Studied the ability of rats to navigate in mazes, rewarding them when they completed the maze without making any mistakes

• Made lesions to the rat’s cerebral cortex and found that more errors were made

What did Lashley discover upon conducting his rat maze experiments?

The number of errors made in navigating the maze was proportional to the size of the cortical lesion, but not its location in the cortex —> memory is not localized to any particular region of the cerebrum

Donald Hebb

• Suggested that networks of many neurons extending throughout the cerebral cortex represent the information stored in memory

• Memory is distributed, and large portions of the brain work together in the formation and retrieval of memories

What do memories contain? What do they involve?

Memories contain multiple kinds of sensory and emotional information, and involve different regions of the brain

Henry Molaison

• Underwent the surgical removal of portions of his medial temporal lobe, including the hippocampus, entorhinal cortex, and amygdala from both hemispheres of his brain

• Epilepsy decreased but memory was impaired

What did Henry suffer from immediately after surgery? What did he still have function of?

• Anterograde amnesia, as he was unable to remember any new information for more than a few minutes

• He still had a working memory, engaging in conversation and recalling numbers immediately after hearing them

What is the hippocampus interconnected with? What direction does it interconnect?

All other regions of the cerebral cotex with interconnectivty running in both directions

What does the hippocampus serve as?

As a hub of distributed activation that helps form the networks of cortical neural connections involved in representing memories in the brain

What is the interconnection of the hippocampus and regions of the cerebral cortex central to?

organizing, storing, and consolidating memory

Why is the medial temporal lobe the frequent focus of seizures?

because the hippocampus and regions of the cerebral cortex are interconnected

What could H.M. still learn post-surgery?

nondeclarative memory

Declarative Memories

• Can be brought to mind in words or describable images, including:

  • Semantic Memory - facts and other information-type knowledge

  • Episodic Memory - time and place events from one’s experience

Nondeclarative memory

Procedural memory, classical conditioning, and priming

Procedural Memory

performing a sequence of actions, with knowledge of a task accessible only through performance, by actually enganging in the actions

Classical Conditioning

Learning to associate certain stimuli and responses, we learn without awareness of what we are learning

Priming

exposure to a stimulus influences one’s response to future exposures to this stimulus

What is LTM captured in?

In the complex interconnectivity of neurons, such that changes in connections change the patterns of activity that occur across the cerebral cortex

Hebbian Network

• Signal activity in networks of neurons serves to strengthen synaptic connections between the neurons —> provides a mechanism for memory storage

• Repeated activation of a network strengthens synaptic connections within the network

What are the ways that signal strength between neurons can be enhanced?

• Increasing the amount of neurotransmitters released from the presynaptic axon terminal

• Decreasing the efficacy of neurotransmitter reuptake by reducing the number of reuptake transporters

• Increasing the number of postsynaptic neurotransmitter receptors

Eric Kandel

• Investigated cellular and molecular changes that underlie memory formation using sea slugs

• Described molecular mechanisms related to the short-term and long-term strengthening of synapses regulating the reflexive behavior of gill withdrawal

What happens if you stimulate a sea slug’s tail region while also touching its siphon?

• Increased robustness of gill withdrawal in response to touching

• Increased robustness is linked to transient strengthening of the synaptic connection linking the siphon neurons with the motor neurons mediating gill retraction

What does the sensory signal registering sensory stimulus to the tail lead to?

The release of serotonin that activates serotonin receptors located on the axon terminals of sensory neurons from the siphon

After just one aversive stimulus being applied to the tail, how long does robust gill retraction last?

after just ONE stimulation, the robustness of gill withdrawal response lasts an hour— this is a short-term memory

After having repeatedly stimulated the tail region, how long does robust gill retraction last?

Repetition results in strengthening, so the robustness of gill withdrawal lasts for many days as a kind of long-term memory