Transcript Ch24- Memory Systems - Biology Courses Server

Neuroscience: Exploring the
Brain, 3e
Chapter 24: Memory Systems
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Introduction
• Learning: Lifelong adaptation to environment
• Several similarities between experience dependent brain
development and learning
– Similar mechanisms at different times and in different
cortical areas
• Memories range from stated facts to ingrained motor patterns
• Anatomy: Several memory systems
– Evident from brain lesions
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Types of Memory and Amnesia
• Learning: Acquisition of new information
• Memory: Retention of learned information
• Declarative memory (explicit)
– Facts and events
• Nondeclarative memory (implicit)
– Procedural memory- skills, habits
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Types of Memory and Amnesia
• Long-Term, Short-Term, and Working Memory
Sensory
information
Short-term
memory
Consolidation
Long-term
memory
Short-term memory
Sensory
information
Consolidation
Long-term
memory
Time
– Working memory: Temporary information storage
requiring rehearsal
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Types of Memory and Amnesia
• Amnesia
– Retrograde amnesia: Forget things you already knew
– Anterograde amnesia: Inability to form new
memories
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The Search for the Engram
• Lashley’s Studies of Maze Learning in Rats
Engram:
memory trace
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The Search for the Engram
• Hebb and the Cell Assembly
– External events are represented by cortical cells
– Cells reciprocally interconnected reverberation
– Active neurons—cell assembly
• Consolidation by “growth process”
• “Fire together, wire together”
– Hebb and the engram
• Widely distributed among linked cells in the
assembly
• Could involve neurons involved in sensation and
perception
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The Search for the Engram
• Hebb’s Cell Assembly and
Memory Storage
Hypothesis
• Distributed Memory
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The Search for the Engram
• Localization of Declarative Memories in the Neocortex
– Inferotemporal Cortex (area IT), higher-order visual
area in macaques
– Lesion impairs discrimination task despite intact visual
system at lower levels
– Disruption of memory or visual pattern recognition?
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The Search for the Engram
• Localization of Declarative Memories in the Neocortex
– At first, all cells respond to newly presented faces
the same amount
– With repeated exposures, some faces evoke a
greater response than others - i.e., cells become
more selective
(Adapted from Rolls et al., 1989 Exp Brain Res 76:153-164, Figure 1.)
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The Search for the Engram
• Electrical Stimulation of the Human Temporal Lobes
– Temporal lobe stimulation
• Different from stimulation of other areas of neocortex
– Penfield’s experiments
• Stimulation -> Sensations like hallucinations, recall past
experiences
– Temporal lobe: Role in memory storage
– Caveat: Minority of patients, all had epilepsy
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The Temporal Lobes and Declarative Memory
• The Effects of Temporal Lobectomy (HM)
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The Temporal Lobes and Declarative Memory
• The Medial Temporal Lobes and Declarative Memory
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The Temporal Lobes and Declarative Memory
• The Effects of Temporal Lobectomy (HM)
– Removal of temporal lobes had no effect on perception,
intelligence, personality
– Anterograde amnesia so profound could not perform basic
human activities (and partial retrograde amnesia)
– Never recognized Brenda Milner, who had studied him for
nearly 50 years
– Impaired declarative memory, but spared procedural
memory (mirror drawing)
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The Temporal Lobes and Declarative Memory
• The Medial Temporal Lobes and Declarative Memory
–
Information flow through medial temporal lobe
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The Temporal Lobes and Declarative
Memory
• The Medial Temporal Lobes and Memory Processing
(Cont’d)
– DNMS: Delayed non-match to sample
– Medial temporal lobe structures: Important for
memory consolidation
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The Temporal Lobes and Declarative Memory
• The Medial Temporal Lobes and Memory Processing (Cont’d)
– Effect of medial temporal lobe lesions on DNMS
– Recognition memory
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The Temporal Lobes and Declarative Memory
• The Diencephalon and Memory Processing
– Brain regions associated with memory and amnesia
outside the temporal lobe
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The Temporal Lobes and Declarative
Memory
• The Diencephalon and Memory Processing
– Radio technician 1959 accidentally stabbed through
left dorsomedial thalamus with fencing foil
• Less severe but like HM; anterograde and some
retrograde amnesia
– Korsakoff’s Syndrome: Alcoholics - thiamin deficiency
• Symptoms: Confusion, confabulations, severe
memory impairment, apathy, abnormal eye
movements, loss of coordination, tremors
• Lesions to dorsomedial thalamus and mamillary
bodies
– Treatment: Supplemental thiamin
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The Temporal Lobes and Declarative Memory
• Memory Functions of the Hippocampus
– Hippocampal responses to old (familiar) and new stimuli
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The Temporal Lobes and Declarative Memory
• Radial arm maze (a)
– (b) Normal rats go down each arm for food only once, but
with hippocampal lesions revisit arms already explored
– (c) Normal and lesioned rats learn which arms are baited
and avoid the rest, but still revisit arms (don’t remember
that they have already taken the food from the arm).
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The Temporal Lobes and Declarative Memory
• Spatial Memory and Hippocampal Place Cells
•Morris water maze:
requires NMDA receptors in
hippocampus.
•Place cells fire when
animal is in a specific
place.
•Dynamic: Place fields
develop as rat becomes
familiar with environment
•Do ‘Place cells’ really
code for place?
Linear maze; restraint
experiments
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The Temporal Lobes and Declarative Memory
• Spatial Memory and Hippocampal Place Cells
– PET imaging in human brain related to spatial navigation
of a virtual town
– Single neuron recording (Epilepsy patients)- ‘place cells’
exist in human hippocampus
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The Striatum and Procedural Memory
• Caudate nucleus + Putamen = Striatum
– Lesions to striatum disrupt procedural memory (habit
learning)
– Standard radial arm maze depends on hippocampus
– Modified radial arm maze, with lighted arms, depends on
striatum; learn assoc. (food at lighted arms).
• Damaged hippocampal system: Degraded performance
on standard maze task
• Damaged striatum: Impaired performance of the
modified task; Double dissociation
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The Striatum and Procedural Memory
• Habit Learning in Humans and Nonhuman Primates
– Parkinson’s patients show that human striatum plays a
role in procedural memory
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The Neocortex and Working Memory
• The Prefrontal Cortex and Working Memory
– Primates have a large frontal lobe
– Function of prefrontal cortex: self-awareness,
capacity for planning and problem solving
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The Neocortex and Working Memory
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The Neocortex and Working Memory
• The Prefrontal Cortex and Working Memory
– Working memory activity in monkey prefrontal cortex
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The Neocortex and Working Memory
• The Prefrontal Cortex and Working Memory
– Wisconsin card-sorting task
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The Neocortex and Working Memory
• The Prefrontal Cortex and
Working Memory (Cont’d)
– Imaging Working Memory in
the Human Brain
– Six frontal lobe areas show
sustained activity correlated
with working memory
– Blue: Facial memory
– Green: Facial and spatial
memory
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The Neocortex and Working Memory
• Lateral Intraparietal Cortex (Area LIP) and Working Memory
– Area LIP: Guiding eye movements -Delayed-saccade task
– Like ‘QV’ cells in S.C.- activity ‘holds’ motor error info
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Concluding Remarks
• Learning and memory
– Occur throughout the brain
• Memories
– Duration, kind of information stored, and brain structures
involved
– Distinct types of memory
– Different types of amnesia
• Multiple brain systems for memory storage
• Engrams in temporal lobe neocortex
– Physiological basis?
– Long-term memories: structural basis?
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End of Presentation
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Types of Memory and Amnesia
• Amnesia: Serious loss of memory and/or ability to learn
• Causes: Concussion, chronic alcoholism,
encephalitis, brain tumor, stroke
– Limited amnesia (common)
– Dissociated amnesia: No other cognitive deficit (rare)
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Types of Memory and Amnesia
• Amnesia (Cont’d)
– Transient global amnesia: Shorter period, temporary
ischemia (e.g., severe blow to head)
– Symptoms: Disoriented, ask same questions
repeatedly; Attacks subside in couple of hours;
Permanent memory gap
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The Search for the Engram
• Localization of Declarative Memories in the Neocortex
– Human extrastriate cortex differentially activated
in car and bird experts
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