Ch.12 Learning & Memory

Where are memories stored in the brain

• The terms ‘LEARNING AND MEMORY’ are so often paired that it sometimes seems as if one necessarily implies the other

  • We cannot be sure that learning has occurred unless a memory can be elicited later

• Early studies by Lashley & Penfield attempted TO FIND A LOCUS FOR WHERE MEMORIES ARE SORED

  • Later research confirmed that memories are stored throughout the brain in a distributed fashion, wherever the events are processed

Amnesia

• Many kinds of brain damage, caused by disease or accident, impair learning & memory by causing amnesia

• AMNESIA is the loss of memory

  • ANTEROGRADE AMNESIA refers to the inability to form NEW MEMORIES AFTER THE EVENT that caused the amnesia

  • RETROGRADE AMNESIA refers to MEMORY LOSS FOR INFORMATION OCCURRING PRIOR TO THE EVENT that caused the amnesia

• Studies of amnesia patients help to clarify the distinctions among different kinds of memories & their mechanisms

The Case History of HM

• In 1953, a patient, named HM, underwent an experimental brain operation at the Hartford Hospital to relieve his seizure disorder

  • William Scoville was the surgeon, who was very much influenced by Penfield who had done similar surgeries

• Immediately after the operation, HM showed a profound ANTEROGRADE AMNESIA

  • Hiss memory was “pure” & not accompanied by intellectual or personality disorders

• To better understand the brain structures required for memory, HM became the topic of intense scientific study for more than five decades

Case of HM PT.2

• The surgery was a bilateral temporal lobe resection, which included hippocampus, amygdala & some surrounding temporal cortex

• After the surgery, he appeared NO LONGER ABLE TO ESTABLISH NEW MEMORIES for events in his everyday life or to learn new information

• But HM was not completely devoid of all memory

  • In fact, his short term memory (ST) was good; and his long term memory (LTM) for childhood events was good

Role of Hippocampus in Memory

• The HIPPOCAMPUS [and not the amygdala] was implicated in the HM because other surgical patients, who had bilateral damage to the amygdala, did not exhibit memory impairment

• These findings suggested that the HIPPOCAMPUS MAY BE NECESSARY FOR FORMING NEW MEMORIES (i.e. consolidation)

• Thus a massive effort was undertaken to understand the role of the hippocampus

Basic Memory Processes

• Since the case of HM, studies have show that a functional memory system must incorporate 3 stages of information processing:

  • ENCODING of raw information from sensory channels into STM

  • CONSOLODATION/STORAGE of STM traces into a more durable from of memory called LTM

  • RETRIEVAL of stored information for use in future behavior

• Note: a problem with any of these memory processes will lead to FORGETTING

• Ex:

Long Term Memory

• Dr. Brenda Milner, a pioneer in the field of neuropsychology, who worked with Penfield, came to study HM

  • On the basis of her assessments of HM, she was able to demonstrate that LTM was comprised of two different memory systems

• 1) DECLARATIVE (explicit) memory: refers to facts & info acquired through learning

  • We are aware of this information & we can declare or verbalize it to others — this memory deals with “what”

• 2) NON-DECLARATIVE (implicit or procedural memory): is memory about perceptual or motor procedures, demonstrated by performance rather than by conscious recollection — this memory deals with “how”

• The job of the HIPPOCAMPUS is to serve MEMORY CONSOLIDATION for declarative LTM… but info is actually not stored in the hippocampus

Types of Declarative & Non-declarative LTM

• There are two from of DECLARATIVE MEMORY:

  • EPISODIC MEMORY

    • Recalling a specific episode from your life

  • SEMANTIC MEMORY

    • Is knowing the meaning of a word without knowing where or when you learned the word

• There are three forms of NON-DECLARATIVE MEMORY

  • SKILL LEARNING

    • learning to perform a series of procedures that requires motor coordination

  • PRIMING (repetition priming)

    • Exposure to a stimulus facilitates or speeds subsequent responses to the same/similar stimulus

  • CONDITIONING

    • Learning simple associations between two stimuli, or a stimulus with a response

Key Learning Theorists

• Pavlov, Skinner, Watson

• Two learning theories:

  • Classical conditioning & operant conditioning

    • Both use nondeclarative memory

Pavlov: Classical Conditioning

• Pavlov won Nobel prize in 1904 for his work on the physiology of digestion

• Discovered CLASSICAL CONDITIONING in which the pair ring of 2 stimuli changed the response to one of them

  • an UNCONDITIONED STIMULUS (UCS) automatically results in an UNCONDITIONED RESPONSE (UCR)

  • After several pairing of the CONDITIONED STIMULUS (CS) with the UCS, the CONDITIONED RESPONSE (CR) can be elicited by the CS without the UCS being presented

Ex:

Watson & Skinner: Operant Conditioning

• In OPERANT CONDITIONING, responses are followed by reinforcement or punishment that either strengthen or weaken the probability that the behavior will occur in the future

  • POSITIVE & NEGATIVE REINFORCERS are events that increase the probability that the response will occur again

  • PUNISHMENTS are events that decrease the probability that the response will occur again

Ex:

Memory Diagram

Ex of skill learning & non-declarative LTM

• Mirror tracing task

  • Trace a figure with a styles, but can only see the mirror reflection

    • With practice, persons trace the figure more quickly & make fewer errors (departures from the figure)

    • Persons with deficits in nondeclarative LTM willl be unable to show improvement with practice

  • But Milner found that HM showed progressive task improvement

    • She concluded that his non-declarative LTM was intact; thus, HM ONLY HAD A DEFICIT IN DECLARATIVE LTM

Hebb’s Theory of Memory

• Herb (1949) hypothesized that memory has temporal stages

  • Sensory memory

  • short-term memory

  • long-term memory

• The AMOUNT OF TIME that info will be retained & the AMOUNT OF INFO that can be stored varies among the different categories for memory

Sensory Memory

• Briefest memories are called ICONIC MEMORIES (visual) & ECHOIC MEMORIES (auditory)

• Fleeting impressions that vanish in <1sec

• Thought to be residual sensory perceptions

Short-Term Memory (STM)

• If attention is paid to the elements in sensory register, STM retains the info for less than 1 minute

  • You can retain 7 ± 2 items in STM

  • Repetition keeps the info available longer

Long-term Memory (LTM)

• enduring from of memory that lasts days or longer, with very large capacity

Memory Trace

• A persistent change in the brain that reflects the storage of info

Hebb Theory Around Long-Term Memory

• Neuronal activities continue even after the termination of the stimulus → inducing STRUCTURAL CHANGES

• Different neurons are linked via this activity & form neural circuits that can fire in specific patterns with minimal stimulation

Workin memory (Central Executive)

• Is responsible for the transient holding & processing of new & already stored information; integral for reasoning, comprehension, and learning memory

Hippocampus: Context

• Hippocampus is involved in cognitive processing of space, time, & the relationships of external cues occurring at the time of an event… CONTEXTUAL LEARNING

  • I.e., remembering the detail & context of an event

Hippocampus: Spatial Mapping & Navigation

• Hippocampal pyramidal neurons recorded exploring an open space exhibit “BORDER, PLACE & GRID FIELDS”

• These cells serve to generate a mental representation of the spatial layout of an environment, known as a COGNITIVE MAP

• BORDER OR BOUNDARY CELLS fire when a person is located near the geographic limit of the space they are in

• PLACE CELLS fire when a person occupies a particular location relative to the arrangement of object within an environment

• GRID CELLS fire when a person is in, or moving toward, a location

Figure Depicting Functional Maps of Hippocampus

Other Cortical & Subcortical Areas Involved in Learning & Memory

• Prefrontal Cortex & Anterior Cingulate Cortex

• Parietal lobe 2^O cortex

• Anterior & Inferior Region of the Temporal Cortex

Prefrontal Cortex & Anterior Cingulate Cortex

• Are linked with learning about rewards & punishments

Parietal lobe 2^O cortex

• Associated with the piecing sensory (e.g., 2^O visual) & motor information together (e.g., dorsal pathway)

Anterior & Inferior Region of the Temporal Cortex

• Is associated with semantic memory (meaning of words) & object recognition (e.g., ventral pathway)

The Neural Basis of Learning in the Nervous System

• ERIC KANDEL

  • Won the 2000 Nobel prize in physiology or medicine for his 1960-80’s research on the physiological basis of memory in storage neurons

  • Studied 3 forms of learning

    • Habituation

    • Sensitization

    • Classical Conditioning

• APLYSIA:

  • Kandel studied the gill & siphon withdrawal reflexes because of the simplicity & relatively large size of the neural circuitry

    • Results: provided solid evidence for the mechanistic basis of learning as “a change in the functional effectiveness of previously existing excitatory connections

• In learning, a HEBBIAN SYNAPSE occurs when:

  • The successful stimulation of a cell by axon leads to the enhanced ability to stimulate the cell in the future

The Neural Basis of learning in the Nervous System (Chemical Explanation)

• Biochemical mechanisms of LTP are known to depend on changes at GLUTAMATE RECEPTORS (AMPA & NMDA) primarily in the postsynaptic neuron

  • Adjacent to the AMPA receptors, magnesium (Mg) ions normally block the NMDA receptors

  • Repeated glutamate excitation of AMPA receptors depolarizes the membrane (Na+ enters)

The Neural Basis of learning in the Nervous System (Chemical Explanation) Pt. 2

• Right panel: The depolarizationat the AMPA channels displaces the Mg ions from blocking the NMDA receptors

• Glutamate is then able to excite the NMDA receptors, opening a channel for Ca+++ & Na+ ions to enter the neuron

• Repeated Ca+++ entry though the NMDA channel triggers protein synthesis that induces production of more AMPA & NMDA receptors

In sum, learning & memory involves tow things:

1. SHORT-TERM changes:

   1. Decreased action potential threshold

   2. Increased neurotransmitter release

   3. Increased number of receptors (LTP)

2. LONG-TERM CHANGES:

   1. Collateral sprouting & axonal branching to increase number of synapses