Transcript feature analyzers in the brain

PART 2: SENSORY WORLDS
#10: FEATURE ANALYSIS IN TOADS II
 recognition & localization of predators &
prey
 feature analyzers in the brain
 from recognition to response
 summary
PART 2: SENSORY WORLDS
#10: FEATURE ANALYSIS IN TOADS II
 recognition & localization of predators &
prey
 feature analyzers in the brain
 from recognition to response
 summary
FEATURE ANALYZERS IN THE BRAIN
 thalamic-pretectal neuron responses to relevant
stimuli
 many classes of neurons respond, but...
 no profiles
p.109 fig.4.10
~ behavior...
 eg, TH3 cells
FEATURE ANALYZERS IN THE BRAIN
 tectal neuron responses to relevant stimuli
 many classes of neurons respond
 T5(1) & (2) interesting
 T5(1) squares >
worms
 T5(2) worms >
squares
 each  20°- 30° of
entire visual field
p.110 fig.4.11
FEATURE ANALYZERS IN THE BRAIN
 tectal neuron responses to relevant stimuli
 T5(2) neurons also showed invariance with
 contrast
 velocity
 distance
 T5(2) are candidate prey-recognition neurons
 ~ same configural detection rules as
behavior
 good eg of neural correlate of behavior
FEATURE ANALYZERS IN THE BRAIN
 tectal neuron responses to relevant stimuli
 remaining questions about T5(2) neurons
perform
prey recognition function (addressed next time...)
 how are they wired into nervous system ?
 further evidence for proposed function ?
FEATURE ANALYZERS IN THE BRAIN
 ganglion cells, contralateral projections  OT & TP
 orderly maps  retinotopic projections
 neuron classes (R16)
p.105 fig.4.7
p.103 fig.4.5
FEATURE ANALYZERS IN THE BRAIN
 tectal neuron responses to relevant stimuli
 remaining questions about T5(2) neurons
perform
prey recognition function (addressed next time...)
 how are they wired into nervous system ?
 further evidence for proposed function ?
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 main determinants of neuron response
properties
of excitatory / inhibitory input
 timing
 magnetude
 what are the sources of T5(2) cell inputs ?
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 TP inhibition of T5(2) neurons in OT
 diagonal moving stimulus...
p.111 fig.4.12
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 TP inhibition of T5(2) neurons in OT
 diagonal moving stimulus  excitation
p.111 fig.4.12
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 TP inhibition of T5(2) neurons in OT
 diagonal moving stimulus  excitation
 + electrical stimulation of TP  inhibition
p.111 fig.4.12
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 TP inhibition of T5(2) neurons in OT
 diagonal moving stimulus  excitation
 + electrical stimulation of TP  inhibition
 remove electrical stimulation  excitation
p.111 fig.4.12
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 TP inhibition of T5(2) neurons in OT
 OT excitation of TP neurons (no details...
reverse experiment likely did not give reverse results)
p.111 fig.4.12
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 TP inhibition of T5(2) neurons in OT 
avoidance ?
 OT excitation of TP neurons  orienting ?
p.111 fig.4.12
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 connectivity possibilities
TH3
TP OT
T5(2)
 what would happen... ?
 feedback loop  oscillator
 what about T5(2) feature analyzer output ?
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 proposed connectivity
T5(1)
T5(2)
TH3
 rationale not immediately clear
 let’s examine this hypothesis anyway...
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 recall response profiles of all 3 types of
neurons
 TH3... (in TP)
 T5(1)... (in OT)
 T5(2)... (putative feature analyzers in OT)
p.113 fig.4.13
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 consider the relative effects of a worm
stimulus...
 TH3  does not inhibit
 T5(1)  does excite
 T5(2)  net effect... excited about worms
p.113 fig.4.13
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 consider the relative effects of the antiworm...
 TH3  does inhibit
 T5(1)  does not excite
 T5(2)  not excited about the antiworm
stimulus
p.113 fig.4.13
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 consider the relative effects of the square...
 TH3  does inhibit
 T5(1)  does excite
 T5(2)  moderately excited about squares
p.113 fig.4.13
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 neuron firing in the hypothetical circuit
(schematic)
 worm
 antiworm
 sm square
 lg square
 recall EFR & IFR
p.113 fig.4.13
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 PT inhibitory signals  OT for T5(2) response
 disrupt PT should
block inhibition
p.113 fig.4.13
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 no lesion... intact PT
 lesion in PT
 2 things happen
to T5(2) response
1.no inhibition
2.selectivity lost
p.114 fig.4.14
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 lesion in PT
 profiles of T5(2) firing (B) = behavior (C)
p.114 fig.4.14
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 increased responses to “inappropriate” stimuli
 termed disinhibition syndrome
 orienting & snapping at non-prey items:
 other toads
 experimenter
 own extremities
FEATURE ANALYZERS IN THE BRAIN
 neural circuit for feature analysis
 T5(2) = feature analyzer neurons in preycatching
 further evidence
 inter- & intracellular recordings
 during behavior
 neurons fire while animals orient
 stimulate same neuron  same orientation
 ok then... how do T5(2) neurons  motor centers
 final section of chapter
FROM RECOGNITION TO RESPONSE
 motor centers: bulbar-spinal region of brain
 OT (T5(2) & other) neurons project  BS region
 stimulate BS region  spike in T5(2) neurons*
 dye-fill T5(2)  see projections into BS region
* opposite to the normal
direction of information
flow... “antidromic” (?)
FROM RECOGNITION TO RESPONSE
 adaptive motor response model
 sensory-motor interface: command-releasing
systems (CRSs)
 made of command
elements (CEs)...
eg, T5(2) & TH3
 motor program
generators (MPGs)
p.116 fig.4.15
FROM RECOGNITION TO RESPONSE
p.97 fig.4.1
 adaptive motor response model
p.116 fig.4.15
FROM RECOGNITION TO RESPONSE
 adaptive motor response model
 specific responses of feature detector neurons
 behavioral experiments
 anatomical analyses of brain structures
 physiological analyses of PT & OT neurons
 initial concept incorrect...
 response not from single aspect of stimulus
 configuration of stimuli... sign stimuli ~ prey
 assemblies of filtering / triggering elements
SUMMARY: SENSORY WORLDS
 input specialization
 conversion of physical stimulus  neural
signal
 acoustic fovea on basilar membrane in bat
 visual fovea in front of toad
SUMMARY: SENSORY WORLDS
 receptive field of a neuron
 source of stimulus and/or representation on
sensory surface (e.g. basilar membrane or retina)
 center/surround; excite/inhibit
 auditory difficult, achieved by neural
processing
 essential aspect of receptive fields 
contrast
SUMMARY: SENSORY WORLDS
 tuning
 sensory neurons respond to part of stimulus
range
 many differently tuned neurons cover whole
range
 achieves gain in sensitivity > broad tuned
system
SUMMARY: SENSORY WORLDS
 maps
 sensory world represented in brain map
 toad: retina tectum
 owl: auditory world ICX
 bat: distance/velocity profiles cortex
 3 common features:
 topography: near-neighbor relationships
preserved; tonotopy, retinotopy
 distortion: fovea overrepresented
 alignment: multimodal maps coincide
SUMMARY: SENSORY WORLDS
 abstraction
 aspects of stimuli are perceived separately
 owl: timing & intensity processing
 bat: velocity & distance processing
 how are parts reassembled by the brain ?
 EMERGENT PROPERTIES REALIZED
SUMMARY: SENSORY WORLDS
 feature analyzers
 some neurons respond to complex stimuli
 toad: T5(2) neurons & moving worm stimuli
 bat: cortex neurons & multiple harmonic
echoes
 capture important aspects of behaviorally
relevant
stimuli
SUMMARY: SENSORY WORLDS
 coincidence detection
 post-synaptic neuron responses to coincident
temporal signals
 owl: left/right coincidence in nucleus
laminaris;
also includes concept of delay lines
 unique disparities encoded by multiple delay
lines
 range of disparities represented in neural
network
SUMMARY: SENSORY WORLDS
 exam 1:
R.2.22