1. Chapter 24: Memory Systems
Neuroscience: Exploring the Brain, 4e
Chapter 24: Memory Systems

2. Introduction
Learning and memory: lifelong brain 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 effects of brain lesions

3. 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—motor skills, habits

4. Types of Declarative and Nondeclarative Memory

5. Types of Procedural Memory
A type of nondeclarative memory
Involves learning a motor response
In reaction to sensory input
Occurs in two categories of learning
Nonassociative learning
Associative learning

6. Types of Nonassociative Learning
(a) Habituation (b) Sensitization

7. Associative Learning
Behavior altered by formation of associations between events
In contrast to changed response to a single stimulus
Classical conditioning (Pavlov)
Pairing of unconditional stimulus with conditional stimulus
Instrumental conditioning (Thorndike)
Associate a response with a meaningful stimulus

8. Classical Conditioning

9. Types of Declarative Memory
Working memory
Temporary storage, lasting seconds
Short-term memories—vulnerable to disruption
Facts and events stored in short-term memory
Subset are converted to long-term memories.
Long-term memories
Recalled months or years later
Memory consolidation: process of converting short- to long-term memories

10. Memory Consolidation

11. Amnesia Amnesia: serious loss of memory and/or ability to learn
Causes: concussion, chronic alcoholism, encephalitis, brain tumor, stroke
Limited amnesia (common)—caused by trauma
Dissociated amnesia: no other cognitive deficits (rare)
Retrograde amnesia: memory loss for things prior to brain trauma
Anterograde amnesia: inability to form new memories after brain trauma

12. Amnesia Produced by Trauma to the Brain

13. Amnesia—(cont.) Transient global amnesia
Sudden onset of anterograde amnesia
Lasts a shorter period, from temporary ischemia (e.g., severe blow to head)
Symptoms: disoriented, ask same questions repeatedly; attacks subside in couple of hours; permanent memory gap

14. Working Memory
We pay attention to small fraction of sensory information.
Some sensory information held briefly in working memory.
Small capacity—limited resource
Mostly discarded, some may be converted to long-term memory
A capability of neocortex found in numerous brain locations

15. Prefrontal Cortex and Working Memory
Primates have a large frontal lobe.
Functions of prefrontal cortex: self-awareness, capacity for planning and problem solving

16. Wisconsin Card-Sorting Test
To demonstrate problems associated with prefrontal cortical damage

17. Working Memory Activity in Monkey Prefrontal Cortex

18. Imaging Working Memory in the Human Brain
Numerous brain areas in prefrontal cortex involved in working memory.
PET study: Six frontal lobe areas show sustained activity correlated with working memory.
Identity task
Location task
Unknown whether working memory for other types of information is held in same or different brain areas

19. Human Brain Activity in Two Working Memory Tasks

20. Area LIP and Working Memory
Cortical areas outside frontal lobe also involved in working memory.
Lateral intraparietal cortex (area LIP)
Involved in guiding eye movements
Stimulation causes saccades.
Demonstrated in delayed-saccade task in monkeys
Other modality—specific areas of parietal and temporal cortex have analogous working memory responses

21. LIP Neuron Response in Delayed-Saccade Task

22. The Neocortex and Declarative Memory
Lashley’s rat experiments
Cortical lesions produce memory deficits.
Speculated all cortical areas contribute equally (equipotential)
Equipotential capacity later disproved
But memory engrams can be widely distributed in the brain

23. Hebb and the Cell Assembly
External events are represented in cortical cells.
Cells reciprocally interconnected  reverberation
Simultaneously active neurons—cell assembly
Consolidation by “growth process”
“Fire together, wire together”
Hebb on the engram
Widely distributed among linked cells in the assembly
Could involve neurons involved in sensation and perception

24. Hebb’s Cell Assembly and Memory Storage

25. The Medial Temporal Lobes
Important for consolidation and storage of declarative memories
Demonstrated by:
Electrical stimulation in the temporal lobe
Neural recordings from the temporal lobe

26. Medial Temporal Lobes and Declarative Memory

27. Information Flow through Medial Temporal Lobe

28. Electrical Stimulation of the Human Temporal Lobes
Temporal lobe stimulation
Effects different from stimulation of other areas of neocortex
Penfield’s experiments
Stimulation  sensations like hallucinations or recalling past experiences
Temporal lobe: apparent role in memory storage
Caveat: complex sensations reported by minority of patients, all with abnormal brains (epilepsy)

29. Human Neural Recordings from the Medial Temporal Lobe
Neurons found that preferentially respond to categories
Faces, household objects, outdoor scenes
Invariant neurons—respond to variety of images are structurally or conceptually related
Individual neurons respond selectively to one person’s face.
Many questions remain.

30. The Effects of Temporal Lobectomy (H.M.)

31. Temporal Lobectomy and Amnesia (H.M.)
Removal of temporal lobes had no effect on perception, intelligence, personality.
Anterograde amnesia so profound he could not perform basic human activities (and partial retrograde amnesia)
He could not recognize the doctor who studied him for nearly 50 years.
Impaired declarative memory, but spared procedural memory (mirror drawing)

32. An Animal Model of Human Amnesia
Studies of macaque medial temporal lobe using experimental ablation
Delayed match-to-sample and delayed non-match to sample (DNMS) tests
Recognition memory tasks
Amygdala and hippocampus not significantly involved in recognition memory
Much still unknown about specific brain areas
Collectively, medial temporal structures critical for consolidation of memory

33. Delayed Non-Match to Sample (DNMS) Task
Medial temporal lobe structures shown important for memory consolidation

34. Effect of Medial Temporal Lobe Lesions on DNMS Performance

35. The Diencephalon and Memory Processing

36. The Diencephalon and Memory Processing: The Case of N.A.
Radar technician accidentally stabbed through left dorsomedial thalamus
Less severe amnesia, but like H.M.: anterograde and some retrograde amnesia
Korsakoff’s syndrome: chronic alcoholism—thiamin deficiency
Symptoms: confusion, confabulations, severe memory impairment, apathy
Can lead to lesions in dorsomedial thalamus and mammillary bodies
Suggests mechanisms involved in consolidation distinct from processes that recall memories

37. Memory Functions of the Hippocampal System
Memory formation, retention, retrieval involve system of interconnected brain areas
Hippocampus involved in various memory functions
Binds sensory information for memory consolidation
Supports spatial memory of location of objects of behavioral importance
Involved in storage of memories for some length of time

38. Effects of Hippocampal Lesions in Rats
(a) Normal rats go down each maze arm for food only once - but not with hippocampal lesions
(b) Normal and lesioned rats learn which arms are baited and avoid the rest

39. Spatial Memory and Place Cells
Learning Morris water maze requires hippocampus.
Place cells fire when animal is in a specific place.
Place fields dynamic

40. Place Cells in Humans
PET imaging in human brain related to spatial navigation of a virtual town

41. Grid Cells Identified in rodent neural recordings Unlike place cells
Respond when animal is at multiple locations that form hexagonal grid
Likely also grid cells in human entorhinal cortex
Place cells, grid cells, and hippocampal neurons showing sensitivity for head direction  brain region highly specialized for spatial navigation

42. A Rat Place Cell and a Grid Cell

43. Hippocampal Functions Beyond Spatial Memory
O’Keefe and Nadel: hippocampus specialized for creating spatial map of environment
Apparent important role in spatial memory
Other hippocampal function theories
Important for working memory
Integrates or associates sensory input
Odor discrimination
Hippocampus links different experiences together.

44. Odor Discrimination Experiment

45. Consolidating Memories and Retaining Engrams
Declarative memory formation involves system of interconnected brain structures:
Take in sensory information
Make associations between related information
Consolidate learned information
Store engrams for later recall
Components include hippocampus, cortical areas around hippocampus, diencephalon, neocortex, and more.

46. Two Models of Memory Consolidation
Standard model of memory consolidation
Information from neocortex areas associated with sensory systems sent to medial temporal lobe for processing
Synaptic consolidation, systems consolidation
Multiple trace model of consolidation
Engrams involve neocortex, but even old memories also involve hippocampus.
Multiple memory traces

47. Reconsolidation Rat experiments
Reactivating a memory makes it sensitive to change as when first formed (before consolidation)
Reconsolidation: the reactivation effect
Human reconsolidation experiments
Recalling a memory makes it susceptible to change
Hippocampal activity
Profound implications for treatment of stress associated with unpleasant memories

48. Procedural Memory
Different memory types involve different brain structures.
The striatum involved in habit learning and procedural memory
Caudate nucleus + putamen = striatum
Key location in the motor loop
Input from frontal and parietal cortex
Output to thalamic nuclei and cortical areas involved in movement

49. The Striatum and Procedural Memory in Rats
Lesions in striatum disrupt procedural memory (habit learning) —but not declarative memory
Standard radial arm maze performance (declarative memory) depends on hippocampus.
Modified radial arm maze performance (performance memory) depends on striatum.
Damaged hippocampal system: degraded performance on standard maze task
Damaged striatum: impaired performance of the modified task

50. Habit Learning in Humans and Nonhuman Primates
Effects of selective brain lesions on memory  comparable in rodents and primates.
In monkeys
Striatum damage—effect on performance memory but not declarative memory
Effects of human diseases
Consistent with striatum’s role in procedural memory
Studies of patients with amnesia and Parkinson’s disease

51. Performance of Patients with Amnesia and Parkinson’s Disease

52. Concluding Remarks Learning and memory
Involve changes widely across the brain
Memories classified based on:
Duration
Kind of information stored
Brain structures involved
Physiological basis for memory storage?
Initially held in fragile form
Long-term memories more robust: structural brain changes?