some principles of stimulus evoked cortical dynamics of visual areas
DESCRIPTION
SOME PRINCIPLES OF STIMULUS EVOKED CORTICAL DYNAMICS OF VISUAL AREAS. Per.E.Roland Bashir Ahmed Michel Harvey Akitoshi Hanazawa Calle Undeman David Eriksson Sarah Wehner Sonata Valentiniene. Brain Research, Dept. Neuroscience, Karolinska Institute , Stockholm, Sweden. - PowerPoint PPT PresentationTRANSCRIPT
SOME PRINCIPLES OF STIMULUS EVOKED CORTICAL DYNAMICS OF VISUAL AREAS
Per.E.Roland
Bashir Ahmed
Michel Harvey
Akitoshi Hanazawa
Calle Undeman
David Eriksson
Sarah Wehner
Sonata Valentiniene
Brain Research, Dept. Neuroscience, Karolinska Institute , Stockholm, Sweden
Roland 2002
Neuron computations start by afferent inputs to the synapses (pre- and postsynaptic), propagate into the dendrites, which perform nonlinear operations, and end by producing electrical spike activity, action potential (AP), or no action potentials .
The result of the computation is a spike train. Neurons communicate by APs and transmitter diffusion. No single neuron can drive the brain.
CORTICAL DYNAMICS
Definition: in vivo spatial and temporal organization of computations
and communications by cortical neurons in real time
How do single neurons work together and at which scale ?
Complex dynamic systems are characterized by their
Architecture (invariant for shorter time periods)
And
Their dynamics
Transients induce dynamics which is different from dynamic states
One cannot predict the dynamics form the architecture
Ferret brain (mustela putorius) working at the mesoscopic scale in vivo
The voltage sensitive dye binds to themembranes of all neurons. When themembrane depolarizes, the dye changes conformation < 1s and emit fluorescence at a higher wavelength
Antic et al 1999
We stain the cortex with a Voltage sensitive dye
1. A STATIONARYOBJECT
Stimulus a 133 ms luminance contrast square
25 ms
50 ms
83 ms
133 ms
250 ms
No stim
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Single trial: luminance contrast square exposed for 133 ms, start 0
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
A Small square lasting 83 ms
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Time derivative of population membrane potentials = C inward current
Laminar recording area 17/18 to stationary square in center of field of view
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
The feedback wave
Neurons from area 21,19 and 18 fire to the feedback wave
p < 0.0001
Roland et al. 2006
Single stationary square
The excitatory connexions in the cerebral cortex (Roland 2008)
The spike train elicited by a luminance contrast defined object interacts with the ongoing activity in area 17 and evokes
1. Thalamo-cortical feed-forward firing IV spreading to III and II and inducinga (relative) depolarization in area 17. The onset of firing in the layers goes in the order IV, III, V, II and VI.
2. Lateral spreading of the (relative) depolarization and firing of neurons representing the object background, continuing until feedback (4)
3. Feed-forward (relative) depolarization of areas 19 and 21
4. With a further delay a Feedback wave of (relative) depolarization of most of areas 19,18 and 17 interacting first with the neurons at the 17 object representation to increase and then decrease the membrane potential here and apparently segment the object from background
2. a spreading decrease of excitation from the area 17 object representation
3. And presumably a second broad feed-forward excitation of area 18,19, 21 and higher
The visual system computes scenes rather than objects
2. OBJECT MOTION
UP FROM PERIPHERYUP FROM PERIPHERY
DOWN FROM DOWN FROM PERIPHERYPERIPHERY
t3-t4
t1-t2
ObjectBackgroundx,y
x,y ds/dt
All that is mapped on the cortex is mapped with a Delay 40 ms
Retina stationary
So how can animals & humans ever catch or avoid an object?
Ferret visual cortex
A MOVING OBJECT WILL BE MAPPED IN MANY VISUAL AREAS
2 x 1O bar moving upwards
Harvey et al subm
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
UP FROM PERIPHUP FROM PERIPH
DOWN FROM PERIPHDOWN FROM PERIPH
1. 1. STATIONARYSTATIONARY
DOWN FROM PERIPHDOWN FROM PERIPH
25º/sec 824ms25º/sec 824ms
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Membrane potentials form layers I-III; Firing from layer IV
DOWN FROM PERIPHDOWN FROM PERIPH
25º/sec 824ms25º/sec 824ms
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Membrane potentials from layers I-III. Firing from layers V-VI
Moving objects on the retina are mapped, with a delay of ~50 ms,moving in retinotopic organized visual areas.
Area 17/18 send feed-forward the object motion to areas 19/21 (layer IV).
In the examples of linear motion, area 19/21 compute a prediction of the future trajectory of the object after ~ 130 ms.
This prediction is sent as feedback to area 17 (layers V VI) instructing area 17 neurons to compute similar prediction and predepolarizing the future cortical path.
The prediction maps the future position 250 ms ahead of the object’s position in cortex.
This gives the animal (human) sufficient time to saccade or prepareand execute limb movement.
Meanwhile, the object mappings move over the cortex in phase, due to the predepolarization in area 17
3. APPARENT MOTION
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Apparentmotion
Ahmed et al. 2008
Apparent motion, population membrane potential
Ahmed et al. 2008
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Ahmed et al. 2008
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
The square is first mapped as stationary until 116 ms
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Ahmed et al. 2008
Split motion
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
d(V(t)rel,AM-V(t)rel;sum)/dt or the difference in dynamics between AM signaland the sum of signals to stationary single squares at identical positions and times
Ahmed et al. 2008
Ahmed et al. 2008
Signals that humans perceive as moving objects. When the identical Square stimuli are shown to the ferret, The square stimuli are initially mapped in area 17 as stationary, but
Time-locked to the offset of the first square1. The mapping of the square in area 19/21 moves towards the
second square 2. A feedback signal from area 19/21 instructs area 17 to
depolarize the path in the direction of apparent motion and 3. The mapping of the square in area 17 moves towards the site
of the next square
The mapping of the square in 19/21 was computed as moving, but computed as stationary in area 17. This discrepancy elicit a feedback from the higher order area forcing are 17 to compute objectmotion
At the mesoscopic scale, the cerebral cortex is well behavedIn real time studies
Communications are reflected in changes of the membrane potentials of the target populations of neurons Examples of communications: feed-forward, feedback with different messages, lateral spreading depolarizations.
Higher order areas may enslave lower order areas though feedback.
The lateral spreading depolarizations and the feedbacks engage very large neuron populations in all visual areas so far measured.
For stationary objects the feed-forward -feedback computations are finished < 120-130 ms. For moving objectsthe computations and communications goes on.
General conclusions (so far)
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Temporal derivative of population membrane potentials, d(∆V(t))/dt, of all animals aligned to cytoarchitectural borders: area 19/21 teaching area 17 the prediction
A: single square at 3 positions in 3 different trials
B: apparent motion, square successively at the 3 positions initially mapped as stationary
The offset ofshort duration stimulielicit a decrease inthe inward currentthat postpones the OFF response
ConsequentlyThe time intervalBetween the ONand OFF firing peakIs prolonged forStimuli < 100 ms
r(t) firing rate