233 Brain

1
Basic neuroscience Perception
J. Lauwereyns, Ph.D. Professor Graduate School of
Systems Life Sciences Kyushu University jan_at_sls.k
yushu-u.ac.jp
2
What do sensory systems do?

• Information about the world
• Each system responds in a specific way
• to a stimulus
• They use specialized cells, peripheral receptors
• Transduce the energy
• Into a change in membrane potential
• Represent stimulus in a signal that all neurons
  can use
• Same currency, action potentials

3

• Different stimulus energies
• (Platypus)
•  

Electroreception through sensitive bill
4

• Different stimulus qualities
• (Bees, dolphins)
•  
• Separate groups of neurons 
• Constantly updating

5
(No Transcript)
6
Rubin vase

• Interaction between
•   Ascending, stimulus-driven
• Descending, goal-oriented
• (Focusing attention)
•  
• This interplay shows
• Difference between sensation and perception

7
Psychophysics

• The quantitative relationship
• between a stimulus and a sensation
• A typical sigmoid function

8
Neuroscience in the 21st century Connecting
psychophysical measures to neural activity
Work by Bill Newsome, Mike Shadlen, etc.
e.g. Motion coherence stimuli
9
Neuroscience in the 21st century Connecting
psychophysical measures to neural activity
Effect of motion coherence on behaviour
Effect of motion coherence on neural
activity
10
Sensory neurons

• Get from physical energy to action potentials

11
Receptors

• Specific for a narrow range of input
• Vary across sensory systems
• All lead to a change in
• membrane voltage
• photoreceptors
• closure of Na channels
• hyperpolarizing
• mechanoreceptors
• opening of Na channels
• depolarizing

12
(No Transcript)
13
Common anatomical plan

• Cross the midline on the way to thalamus
• (To modality-specific thalamic nuclei)
• And then onto primary sensory areas
• Six layers
• III and IV receive axons from thalamus
• (granular cortex)
• From layers III and IV, projections onto other
  layers
• II Ipsilateral (feed forward)
• III Contralateral (unified percept)
• V Spinal cord etc. (motor control)
• VI Back to thalamus (focusing)

14
Vision
15
Structure of the eye
16
(No Transcript)
17
(No Transcript)
18
Phototransduction

• Photopigments in outer segment
• Stimulated by light (bleaching)
• Activates G-proteins (transducin)
• In turn activates effector enzyme
  (phosphodiesterase, PDE)
• Decreases cytoplasmic concentration of 2nd
  messenger molecule (cyclic GMP)
• Ion (sodium) channel in membrane closes
• Membrane potential hyperpolarizes

19

• Centre of the eye fovea
• Surround parafovea
• In the fovea different distribution of
  photoreceptors than in the parafovea
• (in fovea more cones than rods)

20
(No Transcript)
21
(CFF critical flicker fusion do you notice
on/off-switching?)
22
Colour vision 3 types of cones
23
(No Transcript)
24
Example of an On ganglion cell
Stimulus
Neurons response
25
Example of an On ganglion cell
Stimulus
Neurons response
26
Example of an Off ganglion cell
27
(No Transcript)
28
Two streams of visual information

• Starts in the retina with rods vs. cones
• Maps onto Lateral Geniculate Nucleus
• Magnocellular pathway
• Larger receptive fields
• More sensitive in the dark
• (rods)
• Parvocellular pathway
• Acuity, spatial resolution
• Colour
• (cones)

29
Parvo vs. Magno inLateral Geniculate Nucleus
30
(No Transcript)
31
From simple to complex

• Converging input from multiple cells in the
  previous layer onto the next
• Hierarchical organisation
• Analogy of pixel grouping into letters, etc.
• Build-up of selective responsiveness
• LGN
• light at one particular location
• Primary Visual Cortex
• bar of a certain length in a small region
• Secondary Visual Cortex
• bar of a certain length moving in a particular
  direction in 3D in the contralateral hemifield

32
Important characteristics

• Modular organisation
• Each module is dedicated for a specific aspect
  (feature) of the visual information
• Ventral
• Projects to Inferotemporal cortex, IT
• What
• Colour, shape, texture
• Dorsal
• Projects to Parietal cortex, MT, LIP
• Where
• Motion direction, location, orientation

33
Dorsal dysfunction Motion agnosia, inability to
perceive motion
e.g., Unable to see whether cars are
moving or standing still
?
How do I put this thing in that slot?
Damage to area MT (Medial Temporal) Module in
the dorsal stream
34
Ventral dysfunction Prosopagnosia, Face blindness