Systems Physiology II 6010

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Systems Physiology II 6010
Lecture 15 Gain Field Modulation
Bradley Greger, PhD
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Announcements

• Evoked potentials lab move to MEG scanner
• No class Tuesday, April 8th
• Presentations will be two per hour
• Check website for order of presentation
• Have papers chosen by next Tuesday at the latest

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The representation of information

• Cortical areas encode different types of
  information
• neurons in each cortical area have different
  kinds of response fields
• Response fields are formed during development and
  shaped by learning (LTP LTD)

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Response Fields

• How neurons encode information
• What input (sensory stimulus, movement, thought,
  .) causes a neuron to change its firing rate
• Characterized by preferred direction and tuning
  curve

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Build more complex response fields

• Simple response fields early in the cortical
  processing stream (LGN)
• More complex response fields arise later in the
  cortical processing stream out of convergent
  inputs (V1)
• Feedback and lateral connections also influence
  response fields (center-surround inhibition)

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Extremely complex, multi-modal response fields
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Reactivation of responses fields

• Response fields can be (re-)activated without
  external stimuli
• Likely through one of the many cortical
  sub-cortical loops

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Motor response fields

• Tuning curve for reach direction in space from
  motor cortex cell

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Are response fields enough?
Sensory Input
Motor Output
Sensory Response Field
Motor Response Field

• Very reflexive
• Non-dynamic
• Limited utility, decoding neural information

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Are response fields enough?
Modulatory Inputs
Sensory Input
Motor Output
Sensory Response Field
Motor Response Field

• Are there modulatory inputs from other cortical
  areas that can influence information processing?

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Pubmed

• http//www.bioen.utah.edu/faculty/greger/
• From campus network can access many full-text
  papers
• Let me know if you cant get the paper you want
• Can always go to the library and photocopy it
• Search
• receptive field monkey (1594 hits)
• Limit by journal
• Science
• Nature
• Neuron
• Journal of Neuroscience
• Journal of Neurophysiology
• Cerebral Cortex, Hippocampus,

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Encoding of spatial location by posterior
parietal neurons

• Methods
• Extra-cellular single neuron recordings
• Recording action potentials
• Posterior parietal cortex
• where stream

Electrode
Insulated
Uninsulated tip
Neurons
Magnified action potential
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Encoding of spatial location by posterior
parietal neurons

• Methods
• Monkeys were trained to fixate different
  positions on a computer monitor
• The response field of posterior parietal neurons
  were mapped while the monkey fixated several
  different locations

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Encoding of spatial location by posterior
parietal neurons

• Results
• The firing rate of posterior parietals cells, in
  response to a visual stimulus placed in the
  response field, changed with the direction of
  gaze

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Encoding of spatial location by posterior
parietal neurons

• Results
• Tuning curves were generated by placing visual
  stimuli at several locations through the response
  field
• This was repeated for different gaze directions
• The change in firing rate cause by gaze looks
  like a multiplicative gain

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Schematic of gain field modulation
X
Response Field Retinotopic
Gain Field Modulatory input
Gain Modulated Response Field
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Gain Modulation A Major Computational Principle
of the Central Nervous System

• Conclusion
• Gain field modulation provides downstream neurons
  (cortical areas) with information on retinal
  location of stimulus and gaze direction
• This allows calculation of objects location in
  space relative to the body
• Can be extrapolated to very complex relationships
  using tensor calculus

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Memory-guided Movement TaskMedial Intra-parietal
Recordings
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Temporally Extended Reach RelatedNeural Activity
Memory
Motor
Sensory
Spatially Tuned Reach Related Neural Activity
120 Hz
120 Hz
2.7 s
2.7 s
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Saccade Adaptation Task
Back-step Saccade Adaptation

• Back-step of 40 of distance to target
• Random target eccentricities between 7.5 and 22.5
  degrees

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Saccadic Gain as a Measure of Adaptation
Saccade Grain Saccade Distance / Target
Eccentricity
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Saccade Adaptation change gain of movement
Pre-Adaptation
Early Adaptation
Late Adaptation
1.4
1.0
Saccade Gain
0.4
500
1000
Trial Number
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Likely Effects of Saccade Adaptation
Shift in RF location
Firing Rate
Eccentricity (Degrees)
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Likely Effects of Saccade Adaptation
Gain Modulation of RF
Firing Rate
Eccentricity (Degrees)
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Example of Modulated Eccentricity Tuning Curve
Sensory
Memory
Motor
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Example of Modulated Eccentricity Tuning Curve
Sensory
Memory
Motor
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Schematic of change in gain field modulation by
adaptation
Pre-adaptation
X
Post-adaptation
Response Field (retinotopic)
Gain Modulated Response Field
Gain Field
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Are response fields enough?
Gain Field Modulation
Sensory Input
Motor Output
Sensory Response Field
Motor Response Field

• Gain field modulation
• Fundamental neural computation
• Allows for dynamic modulation of neural
  processing by other cortical areas
• Extrapolates into cognitive domain
• hierarchical