Spatial Frequency Spatial Frequency Maps in Cat Visual Maps in Cat Visual

CortexCortex

Naoum P. Issa, Christopher Naoum P. Issa, Christopher Trepel, and Michael P. StrykerTrepel, and Michael P. Stryker

Jasmine Kwong

The QuestionThe Question

What is the fundamental functional What is the fundamental functional organizational unit of the brain?organizational unit of the brain?

---> The organization of orientation selectivity ---> The organization of orientation selectivity has been thoroughly described, but what is the has been thoroughly described, but what is the arrangement of spatial frequency (SF) arrangement of spatial frequency (SF) preference in V1?preference in V1?

Suggested layoutsSuggested layouts

Laminar - layersLaminar - layers Columnar - columnsColumnar - columns Clustered - randomClustered - random Pinwheel - orderedPinwheel - ordered Binary - high and low SFsBinary - high and low SFs

Which one is correct?Which one is correct?

Present stimulus and obtain optical imaging of Present stimulus and obtain optical imaging of intrinsic signalsintrinsic signals

Look at geometry of patterns of images to Look at geometry of patterns of images to examine layout of SF preferenceexamine layout of SF preference

MethodsMethods

Optical imaging of intrinsic signalsOptical imaging of intrinsic signals 7 cats, 7 - 16 weeks old (contrast sensitivity has 7 cats, 7 - 16 weeks old (contrast sensitivity has

reached adult levels), anesthetizedreached adult levels), anesthetized Experiment begins with mapping of orientation Experiment begins with mapping of orientation

and ocular dominance by showing 20 stimulus and ocular dominance by showing 20 stimulus conditionsconditions

Spatial frequency mapping required much more Spatial frequency mapping required much more stimulus conditions, so were distributed among stimulus conditions, so were distributed among either 2 or 4 sets that were run sequentiallyeither 2 or 4 sets that were run sequentially

MethodsMethods

Each stimulus set included a wide range of SFs Each stimulus set included a wide range of SFs and orientations and was designed to provide a and orientations and was designed to provide a coarse map before combination with data from coarse map before combination with data from other setsother sets

A map from 8 orientations and 8 SFs was A map from 8 orientations and 8 SFs was constructed from 4 stimulus sets, each constructed from 4 stimulus sets, each consisting of 22 conditionsconsisting of 22 conditions

MethodsMethods

Additional sporadic multi-unit extracellular Additional sporadic multi-unit extracellular recordings (electrophysiology) to confirm that recordings (electrophysiology) to confirm that optically imaged SF maps correspond to optically imaged SF maps correspond to neuronal SF activityneuronal SF activity

After the experiments, the animal was sacrificed After the experiments, the animal was sacrificed --> Histology of visual cortex (electrode tracks --> Histology of visual cortex (electrode tracks and recording positions reconstructed)and recording positions reconstructed)

ResultsResults Area 18 was well stimulated by the 2 lowest SFs Area 18 was well stimulated by the 2 lowest SFs

presented - 0.1, 0.16 c/degpresented - 0.1, 0.16 c/deg Area 17 was activated by gratings of higher SFArea 17 was activated by gratings of higher SF

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ResultsResults

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ResultsResults

- Regions of cortex respond to narrow ranges of SFs

- there really are domains that prefer intermediate SFs

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ResultsResults SF preference in area 17 is continuous over SF preference in area 17 is continuous over

most of the cortex but has distinct linear most of the cortex but has distinct linear discontinuitiesdiscontinuities

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Relationship Relationship between SF and between SF and

orientationorientation Colocalization of pinwheel Colocalization of pinwheel

centers with domains of extreme centers with domains of extreme SF, low or highSF, low or high

Preferred SF not independent of Preferred SF not independent of stimulus orientation for many stimulus orientation for many single units, BUT…single units, BUT…

Orientation preference changes Orientation preference changes little with stimulus SF --> little with stimulus SF --> orientation preference is primarily orientation preference is primarily independent of stimulus SFindependent of stimulus SF

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ConclusionsConclusionsFour characteristics of organization of SF preference in Four characteristics of organization of SF preference in

V1V1

1)1) Cells with SF preferences between 0.2 and 1.8 c/ Cells with SF preferences between 0.2 and 1.8 c/ are clustered into domains with other cells of similar are clustered into domains with other cells of similar SF preferenceSF preference

2)2) These SF domains are organized into a map that is These SF domains are organized into a map that is locally continuous across V1, though the spatial locally continuous across V1, though the spatial gradient of SF preference is not constant, and there gradient of SF preference is not constant, and there are often clear fractures in the SF map before the are often clear fractures in the SF map before the entire range of SF preference is representedentire range of SF preference is represented

ConclusionsConclusions

3) Distance between domains of very different SF 3) Distance between domains of very different SF preference conforms to the hypercolumn preference conforms to the hypercolumn description of cortical organizationdescription of cortical organization

4) Cortical domains containing cells that prefer 4) Cortical domains containing cells that prefer extremes of SF continuum tend to colocalize extremes of SF continuum tend to colocalize with pinwheel centers in cortical map of with pinwheel centers in cortical map of orientation preferenceorientation preference

ProblemsProblems

Anesthetized cats (changes cortical properties)Anesthetized cats (changes cortical properties) Low Signal to noise ratio of method --> Need to Low Signal to noise ratio of method --> Need to

average pictures. Controversial. More than one average pictures. Controversial. More than one way to do it. Arbitrary? Can create artifacts.way to do it. Arbitrary? Can create artifacts.

Coarse sampling of spatial frequency - only 8.Coarse sampling of spatial frequency - only 8. Though SF preference sometimes varied with Though SF preference sometimes varied with

deeper penetrations into cortex, no systematic deeper penetrations into cortex, no systematic investigation of possibility of laminar investigation of possibility of laminar organization of SForganization of SF