Memory and Amnesia Flashcards
What are learning and memory?
- Lifelong adaptations of brain circuitry to the environment
- Enable us to respond appropriately to situations we have experienced before
- The acquisition of new knowledge and skills
- No single brain system is responsible for learning or memory
- Different brain lesions affect different types of remembered information, suggesting that there must be more than one system
Compare and contrast declarative and nondeclarative memory.
- Declarative
- explicit
- facts and events
- episodic and semantic memories
- conscious recollection
- easily forgotten - Nondeclarative
- implicit
- procedural memory (skills, habits, behaviours, emotional responses)
- unconscious
- takes lots of repetition / time to form
- Not easily forgotten
Compare and contrast the two types of procedural memory.
- Non-associative
- change in behavioural response that occurs over time in response to a single stimulus
- Habituation: Response to the same stimulus decreases over time
- Sensitization: Following a strong sensory stimulus, response to same stimulus increases - Associative
- Behaviour is altered by the formation of associations between events
- Classical conditioning
- Instrumental conditioning
What are the 3 temporal categories of declarative memory?
- Long term memory: Recall days, months, or years after it was originally stored. Not easily disrupted.
- The longer these memories are stored, the less easily they are disrupted. If you suffer brain trauma, earlier memories more likely to be disrupted. - Short-term memory: Information held temporarily (for hours) and are vulnerable to disruption. Easily erased by head trauma, ECT, etc.
- Working memory: Temporary storage (seconds), limited in capacity and unique for each sensory modality. Can be disrupted by shifts in attention.
What is memory consolidation?
- The process of converting STMs into LTMs
- If sensory information is behaviourally relevant, goes from WM to STM
What is amnesia? Distinguish between retrograde and anterograde amnesia.
- Amnesia: A loss of memory and/or inability to learn due to certain diseases and injuries to the brain. Causes you to forget a lot more than you learn.
- Retrograde: Memory loss for events prior to the trauma. You forget things you already knew. Memories of months / years prior to trauma are forgotten while older memories stay strong. This suggests that memories are shifted to different parts of the brain over time and become more secure.
- Anterograde: Inability to form new memories. In severe cases, learning may be completely absent, but it is more common for learning to be slower and require more repetition. Nothing that you already knew was disrupted.
Which brain region is involved in working memory?
- Prefrontal cortex
- Lesions to this area disrupt performance on WM tasks
Explain the delayed response task. What does it reveal about the role of the PFC in WM?
- Present monkey with 5 wells
- One of the wells has food in it
- Curtain is pulled down and covers are placed on the wells
- Wait a certain amount of time before pulling curtain back up
- Monkey has to remember which well the food was in
- After practice, monkey will eventually choose correctly
Found that:
- Some PFC neurons responses while the animal first saw the food wells, was unresponsive during the delay interval, and responded again when the animal saw the food wells again. This suggested a correlation between neuron firing and visual stimulation..
- Other PFC neurons fired only during the delay interval. Thus, activity was not correlated with visual stimulation and may be related to the retention of information needed to make the correct choice after the delay. If these neurons are silenced during the task, animal will make the wrong choice. May represent WM.
How many areas of the frontal lobe become activated during the delay period of a WM task?
six
Explain the identity and spatial tasks and how many areas of the frontal lobe became activated for each.
Identity task
- Subjects shown 3 faces in 3 locations on the screen and are asked to memorize the faces
- Delay of 30, 60, or 90 s
- Face pops up in random location and you are asked if you have seen it before
- If you choose correctly, 3 areas of frontal lobe light up during delay period
Spatial task
- Same as identity task except you are asked to remember spatial location of faces
- If you choose correctly, one area of frontal lobe lights up during delay
- 2 areas were equally active for both tasks
What is the role of the lateral intraparietal cortex in WM? Where is this area located?
- Buried in intraparietal sulcus
- Involved in guiding eye movements
- Electrical stimulation elicits eye saccades to specific regions of the visual field
Explain the delayed saccade task and how area LIP responds to this task.
Task
- During training phase, animal fixates eyes on centre of screen
- Target is flashed somewhere in periphery and there is a delay
- Animal moves eyes to where target was and is rewarded if it does so
- Must remember where target was in order to complete the task
Response
- LIP neurons fire in response to the visual cue but maintain firing throughout the delay period
- Disrupting activity causes success on task to decrease
- Might reflect modality specific WM
What are engrams?
- Location of a memory
- Memory traces
Explain the experiments that Lashley conducted to find memories in the brain. What were his findings? Why were his experiments problematic?
Experiments
- Trained rats on mazes until they were efficient at them
- He then destroyed brain regions to try and see where memories were located
- Paid particular attention to neocortex
- Found that lesions to the rat brain after learning the maze would disrupt performance, thus he apparently damaged or destroyed the memory of the maze
Findings
- Severity of memory deficits was correlated to the size of the lesion, but was unrelated to the location
- Speculated that all cortical areas contributed equally to learning and memory
- Engrams are based on neural changes spread throughout the cortex rather than being localized to a specific area
Problems
- Lesions were very large and damaged multiple areas
- Rats may have solved maze in different ways (e.g., by using different sensory modalities)
- Disrupting performance on maze far stretch from destroying entire memory – rat may still remember the maze but not be as sufficient at it
What did Donald Hebb propose about the cell assembly of declarative memory?
- The internal representation of an object consists of all the cortical cells that are activated by an external stimulus
- Cell assembly: A group of simultaneously active, reciprocally connected neurons
- Internal representation is held in WM so long as activity reverberated through the cell assembly – activity persists after stimulus is removed
- Consolidation occurs if activity of cell assembly crosses a temporal threshold: Lots of APs that occur over time strengthen connections between cells (growth process that makes connections stronger and more effective)
- Neurons become so connected that turning one on turns all of them on – If only one neuron is activated, they all become activated (entire representation of the stimulus with only partial external representation)
