20. Hippocampus and Memory

June 1, 2015 by Dr. Tangen Leave a Comment

I’ve got my thinking cap on. Will it help me remember?

Thinking and memory aren’t the same thing but highly related. Human memory is composed of several systems. It’s not a single process. Memory involves nearly every part of the brain, both sides.

The two hemispheres are connected by the corpus collosum. This bundle of neurons keeps our two super computers in touch with each other. One side names the object that your other side is reaching for. It’s teamwork.

Here’s what is included in this lesson:

Split-brain people
Types of memory and what they do
Implicit memory (dancing without words)
HM

Read chapter 13 of Kalat’s Biological Psychology

Video clip: Elizabeth Loftus on false memories.

Here are the resources you need:

cluster
slides
terms
notes
quiz
video

SLIDES

TERMS

9×9 pixel bit map
ablation
acetylcholine
amnesia
amygdala
anterior cingulate cortex
anterograde amnesia
basal ganglia
bilateral
bilateral damage
coma
competition vs cooperation
componential encoding
conditioned responses
confusion
consolidation
corpus collosum
cortisol
declarative memory (things you know)
delayed-response task
dyslexic children
epilepsy
epinephrine
episodic memory (life story of events)
fabric identification task
fast transmission (myelinated)
fear learning
generalized seizure
genu = anterior (knee)
ginkgo biloba
habit learning
hemisphere independence
hippocampus
HM
implicit memory
Jacuzzi
lateralization of function
left hemisphere
long term memory (LTM)
matching-to-sample task
memory formation
memory loss
mirror drawing task
motor learning
neurotransmitters
non-declarative memory
nonmatching-to-sample task
priming
procedural memory
prospective memory
recall
reconsolidation
rehearsal
retrograde amnesia = before
right hemisphere
rotating disk task
seizures
semantic dementia
semantic memories
semantic memory (names and facts)
sexual dimorphism
short term memory (STM)
sparse encoding
spatial memory
spatially tuned
splenium = posterior portion
split-brain people
temporal lobe cortex
truncus = middle (body)
ventralmedial area of prefrontal cortex of frontal lobe
working memory

NOTES

Memory
- Frontal lobe
  - Prefrontal cortex
    - 3 regions
    - 1. dorsolateral (previously)
    - 2.orbitofrontal (previously)
    - 3. ventralmedial
3. Ventralmedia
- Anterior cingulate cortex
  - Collar around corpus collosum
- Corpus collosum
  - Two Computers
    - Left and Right Hemispheres
  - Each controls contralateral side
    - Except taste and smell
    - Uncrossed
    - Its own side of the tongue
  - Work together
    - Control trunk & facial muscles
    - Staying Connected
  - Corpus Callosum is a set of axons
    - Interconnect hemispheres
    - Exchange information
    - Wide, flat bundle of neural fibers
    - Under cortex
    - Largest white matter structure
    - 200–250 million axons
    - Fast transmission (myelinated)
  - Parts
    - 1. Genu = anterior (knee)
      - Thin axons
      - Connect prefrontal cortexes
      - Larger in musicians
    - 2. Truncus = middle (body)
      - Thick axons
      - Connect motor cortexes
      - M1, premotor & supp. motor
    - 3. Splenium = posterior portion
      - Soatosensory info
      - Parietal lobes
      - Visual cortexes
  - Size
  - Sexual Dimorphism
    - Different size in men & women? No.
  - R. B. Bean,1906
    - Larger is intelligence
    - Men
    - Race
    - Ultimately refuted
  - Larger in left-handed?
    - 11% bigger
  - Dyslexic children have smaller CC
- Childhood
  - Gradually thickens as grow
  - Slow growth until about age 10
  - Eventually develop adult patterns
  - Young children behavior similar to split-brain people
  - Fabric identification task
  - Five-year olds
    - Equally well w/ one or two hand
  - Three-year olds
    - 90% more errors w/ two hands
Lateralization of Function
- Epilepsy
- Seizures = excessively synched neural activity
  - Most treated with drugs (90%)
  - More severe, tissue ablation
  - Extreme, severe CC
- Neural activity rebounds between prolongs seizures
- Called split-brain people
Split-brain people
- Present input of object to L field
  - Info to R hem (noses cross)
  - L hand controlled by R hem
  - Can point to it with L hand
  - Can’t do it with right hand
- Present input of object to R field
  - Info to L hem (noses cross)
  - Can name or describe what see
  - Language in L hem
    - 95% of R-handed
    - 80% of L-handed
- Independence
  - Each hem. can process info
  - Multitask
  - Draw circles
    - One with each hand
    - One hand going faster
  - For a few weeks, feels like two people in one body
- Competition vs Cooperation
  - Take item off grocery self with L
  - Return them with R
  - Eventually
    - Brain uses smaller connection routes to avoid conflicts
    - CC not the only path
    - Just the biggest
- Cooperation
  - Flash different word to each visual field at same time
  - Report combined concept
HM
- Henry Molaison (1926-2008)
- 1 generalized seizure a week
  - began bilaterally
  - in medial aspects of both temporal lobes
- Removed both of H.M.’s medial temporal lobes (in 1953)
  - included most of
  - hippocampus
  - amygdala
  - adjacent temporal cortex
- Post-surgery symptoms
  - Major seizures almost completely eliminated
  - Minor seizures down to 1-2 day
  - IQ increased (104 to 118)
  - Normal short-term memory
  - Moderate retrograde amnesia
    - loss for events shortly before
  - Severe anterograde amnesia
    - memory loss for events after
*******************
- Amnesia
  - Types
  - retrograde amnesia = before
  - anterograde amnesia = after
  - Progression
    - Normal cognition
    - Retrograde amnesia
    - Coma
    - Confusion
    - Anterograde amnesia
    - Normal cognitive function
*******************
HM (more)
- Post-surgery symptoms
  - Can’t transfer anything to LTM
  - Everything is forgotten when attention shifts
  - Impaired ability to form LTM
    - newer words like Jacuzzi and granola regarded as nonsense
  - When distracted
    - underestimate his own age by 10+ years
  - Can’t form episodic memories
    - memories of a single event
    - could describe previously learned facts
    - not recount personal events
  - Retained ability to
    - Weakly retain semantic (factual) memories
    - Difficult to describe the future
HM’s Implicit Memory
- Mirror Drawing
  - First to show improvement in HM
  - Spatial –motor learning
  - Implicit learning
- Rotating Disc
  - Keep pen on target (rotating disk)
  - Improved over 7-day period
  - Each time saw task, claimed he had never seen it before
Hippocampus
- Temporal lobe & Dorsalmedial area of frontal lobe
- Semi-circle
- If damaged, amnesia
  - Remember before & after accident
  - Not accident or around it
- If small damage
  - Retrograde amnesia
  - Can’t remember past
  - Just before accident
- If bilateral damage
  - Anterograde amnesia
  - Can’t form new memories
- Consolidation memory
  - move from short to long term
  - not necessary to retrieve info
  - must work to put into long term
- Reproduces patterns during sleep
  - Encodes patterns
  - Sparse representations (non-overlapping)
  - Sparse encoding allows quick learning
  - Componential encoding
    - 9×9 pixel bit map
    - 81 pixels
    - like cortex
    - efficient
    - good for generalization
  - Sparse encoding uses 13 lines
  - Trains cortex
    - Repeats pattern over time
      - Find L in field of Ts
      - Patterns repeated
      - Ss unaware of pattern
    - Improves over time
      - No “thinking” required
      - Priming
Memory Systems
- Procedural Memory
  - What you can do
- Sensory Memory
  - Buffers for vision & audition
- Prospective Memory
  - Remember what going to do
  - Sensitive to elderly
- Declarative (things you know)
  - Episodic (life story of events)
    - right hemisphere
  - Semantic (names and facts)
    - left hemisphere
Neurotransmitters
- Epinephrine
  - enhances consolidation
  - if blocked, interferes with memory formation
- Cortisol
  - enhances consolidation
  - increase glucose availability?
- Ginkgo Biloba may increase blood flow
- Acetylcholine is necessary to form new declarative memories
Non-Declarative Memory
- Doesn’t use hippocampus
- Non-word learning
- Acquired slowly
- Includes
- conditioned responses
- skills
- habits
- priming
Types of Memory
- Short-term memory
  - Memory of events just occurred
  - About seven items (+-2)
  - Rehearsal to get it in
  - Once gone, lost forever
- Long-term memory
  - Memory of previous events
  - Long-term memory is vast
  - Difficult to estimate how big
  - Rehearsal not needed
  - May recall with hints
- STM can be moved to LTM
  - Held in working memory
  - If score changes, throw out old score
- Consolidation
  - Varies widely between people & material
  - Interesting facts more than boring
  - Emotional items learned quickly
    - Cortisol activates
      - Amygdala
        
        storage of emotional events
      - Hippocampus
        
        Consolidates emotional event
  - LTM not permanent
    - Change, fade & vary in detail
    - Reconsolidate a memory if:
    - A reminder followed by similar experience
    - New experiences during reconsolidation can modify memory
Working Memory
- Temporary storage of tasks
- Attending to right now
- Delayed-response task
  - Ss given signal
  - Give response after a delay
  - Damage to prefrontal cortex
    - Impairs working memory tasks
  - Older people often have impaired working memory
    - Prefrontal cortex may change as age?
Amnesia
- Memory loss
  - Better Implicit Memory
  - Nearly all patients with amnesia show better implicit memory
  - Impact of recent experience on behavior
    - even if not realize using memory at all
  - Not good at deliberate recall
  - Good at doing without knowing
Usually
- better implicit than explicit
- normal working memory
- nearly intact procedural memory
- some retrograde amnesia
- severe anterograde amnesia
Hippocampal damage
- Impairs performance on
  - Delayed matching-to-sample tasks
    - Task used in animals
    - Animals see an object (sample)
    - After a delay choose between two objects
    - Goal: choose one matches the sample
  - Delayed nonmatching-to-sample tasks
    - Same procedure
    - Except animal must choose the different object
Spatial Memory
- Hippocampal neurons
  - spatially tuned
  - to particular spatial locations
- Cab drivers
  - Larger than normal posterior hippocampus
- When answering spatial Qs
  - hippocampus activated
- Need to recall detail & context
- Recent memories have sig detail
- Recalling recent memories
  - activates hippocampus
- Recalling older memories
  - may not require hippocampus
The Basal Ganglia
- Needed for implicit learning
- habit learning
Other Brain Areas in Memory
- Almost all brain involved in some aspect of memory
- Amygdala used in fear learning
Parietal lobe damage
- Affects ability to associate one type of info with another
Temporal lobe damage
- Anterior & inferior lobes results in
- Semantic dementia
- Impaired semantic memories
Prefrontal lobe damage
- Impairs ability to learn about rewards and punishments
Summary
- Don’t lose all aspects of memory equally
- Several somewhat independent kinds of memory
- Each depends on different brain areas

QUIZ

1. Which connects the left and right hemispheres:
- a. corpus collosum
- b. hippocampus
- c. cerebellum
- d. pons
2. Which is needed for habit learning:
- a. demifactoral gyrus
- b. corpus collosum
- c. basal ganglia
- d. amygdala
3. Cab drivers have:
- a. same sized hippocampi as everyone else
- b. smaller hippocampus areas
- c. larger hippocampus areas
- d. inverted basal ganglia
4. Nearly all patients with amnesia have:
- a. more prospective memory damage than semantic
- b. more semantic memory damage than implicit
- c. difficulty remembering their childhood
- d. no memory at all
5. Which is the part of the corpus collosum that connects the left motor cortex to the right one:
- a. nucleus accumbens
- b. splenium
- c. tuncus
- d. genu

For the answers: Click Here

VIDEO