Transcript Slide

Neural mechanisms of
Spatial Learning
Spatial Learning
Materials covered in previous lectures
• Historical development
– Tolman and cognitive maps
• the classic paper 1948 “cognitive maps in rats and men”
• Multiple memory system, Animal models
• Eichenbaum et al (1990), Morris water maze task
– Constant-start-location &
– Variable-start-location
• Kesner et al (1993) (Module 2)
– Spatial location
– Motor response
– Object recognition
Tolman and cognitive maps
Eichenbaum et al (1990)
Morris water maze task
Kesner et al (1993)
(Module 2)
Sensory cues during Navigation
1. external landmarks
1. animals use visual landmarks to guide them to
goal locations
2. idiothetic (self-motion) cues: vestibular cues or
proprioceptive cues
1. The self-motion information can derive both from
internal sources and from external sources (e.g.,
optic flow cues).
Spatial frames of reference
• Allocentric processing
– Relation between objects
– Hippocampaus
• Egocentric processing
– Relation between objects and self
– Caudate etc
Lesion work, brain structure involved …
Ongoing operation of the human hippocampus and
related brain structures during memory performance
•functional neuroimaging methods in normal humans
•Module 5
•recording of the activity patterns of single neurons in animals
•Module 6
Positron emission tomography (PET)
Functional magnetic resonance imaging (fMRI)
1. blood flow and brain oxygen consumption
2. level of activation of a brain area
3. temporal resolution: second
4. spatial resolution: several thousand neurons
1. at only a gross level that tells us which structures
are activated to major shifts in task demands.
5. the simultaneous examination of the entire system
Single cell recording studies in animals
1. monitoring the action potentials of individual neurons
2. the inner workings at the cellular level
3. increase in resolution
1. Spatial resolution: particular types of neurons within a
specific brain structure
2. temporal resolution: millisecond
4. the fundamental coding properties of the units of neural
computation.
5. Drawback: only one part of the system at any time
Landmark studies:
1.Tolman, Cognitive map -
2.O’Keefe, place cells
Hippocampus place cells in rats, early findings
Initial report: O'Keefe and Dostrovsky's (1971)
These neurons fire only when the rat is in a particular
location in its environment and firing is independent of
the rat's orientation or ongoing behaviour.
Place field
Evidence for encoding of spatial relationships
in the environment
1. place fields move in concert with rotation of salient visual cues
2. they scale with enlargement of all features of the environment,
3. Place cell activity can be related to the rat's memory about its
spatial location
Place fields move in concert with rotation of salient visual cues
They scale with enlargement of all features of the environment
Theories
Place cells – cognitive map
O’Keefe and Dostrovksy made the discovery of the
place cell that
“constructs the notion of a place in the environment
by connecting together several multisensory inputs,
each of which can be perceived when the animal is
in a particular part of the environment”
Theories
Alterative theories: Eichenbaum “memory space” model
1.
Place cells fire in response to the complex interaction of
multiple cues and not in response to an internal Cartesian
coordinate system.
2.
patterns of activation are directly related to particular
perceptual, behavioural, and cognitive cues that are being
experienced together, in a particular location, and at a
particular time.
3.
Other factors have been demonstrated to influence the firing
of place cells such as
orientation within an environment,
direction of movement,
speed of movement,
angle of movement,
presence/absence of landmarks,
the intentions related to the movement (e.g., searching for a food
reward).
Neural mechanisms of spatial
processing in rats, recent analysis
Cell types
1. Place cells: hippocampus
2. Head direction cells
1. parts of the thalamus and limbic system
2. fire when the rat’s head is pointed in a
particular direction, regardless of the
animal’s location in the environment or the
position of the body relative to the head.
Response properties for both types of cells
1. Controlled by an interaction between landmarks and idiothetic cues
2. Role of visual landmark (important but not required)
1. rotation of the landmarks -- > an equal rotation of the firing
location/ direction of the place cells or head direction cells
2. maintain their location/ direction tuning for many minutes in total
darkness, provided that the rat had established its bearings
before the light was turned off
3. Role of non-visual input
1. vestibular input does appear to be necessary for these cells to
maintain their selective firing properties
2. influenced by the ‘‘motor set’’ of the animal
3. will shut off or reduce firing dramatically if the rat is restrained
tightly, even if the rat is placed in the proper firing location/
direction of the cell under study