brain areas and topography last update: january 2011 last course: psychology 9224, w2011,...
TRANSCRIPT
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Brain Areas and Topography
http://www.fmri4newbies.com/
Last Update: January 2011Last Course: Psychology 9224, W2011, University of Western Ontario
Jody CulhamBrain and Mind Institute
Department of PsychologyUniversity of Western Ontario
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What Defines an Area?
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Definition of an “Area”
• Neuroimager’s definition of an area: Some blob vaguely in the vicinity (+/- ~3 cm) of where I think it ought to be that lights up for something I think it ought to light up for
• Neuroanatomist’s definition of an area: A circumscribed region of the cerebral cortex in which neurons together serve a specific function, receive connections from the same regions, have a common structural arrangement, and in some cases show a topographic arrangement
• may also be called a cortical field
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Cortical Fields: Anatomical Criteria
1. Function– an area has a unique pattern of responses to different stimuli
2. Architecture– different brain areas show differences between cortical
properties (e.g., thickness of different layers, sensitivity to various dyes)
3. Connectivity– Different areas have different patterns of connections with
other areas
4. Topography– many sensory areas show topography (retinotopy, somatotopy,
tonotopy)– boundaries between topographic maps can indicate
boundaries between areas (e.g., separate maps of visual space in visual areas V1 and V2)
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Macaque Visual Maps
• Over 30 visual areas
• Visual areas make up ~40% of monkey brain
Van Essen et al., 2001
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Brodmann’s Areas
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Brodmann Area 17
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Brodmann Area 17 Meets 21st Century
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Logothetis fMRI data: image from http://www.bruker-biospin.com/imaging_neuroanatomy.html
Anatomical MRI Functional MRI
Goense, Zappe & Logothetis, 2007, MRILayer 4 fMRI activation (0.3 x 0.3 x 2 mm spin echo)
Layer 4
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MT: A Case Study
• Middle temporal area of the macaque monkey• Sometimes also called V5 (5th visual area)• Meets all criteria for an area• Has an apparent human equivalent
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MT: FunctionSingle unit recording
– Single neurons in MT are tuned to the direction of motion
– Neurons are arranged in “direction hypercolumns” within MT cortex
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MT: Function
• Lesions– lesions to MT lead to deficits in perceiving motion
• Microstimulation– stimulation of a neuron affects the perception of motion– e.g., if you find a neuron with a preference for upward motion, and
then use the electrode to stimulate it, the monkey becomes more likely to report “upward” motion
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MT Architecture
• MT is stained with cytochrome oxidase (which indicates high metabolic activity)
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MT Connectivity• MT receives direct
input from V1– largely from the “fast”
magno pathway cells
• MT projects to specific higher-level areas
• MT is an intermediate level visual area
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MT Topography
• MT has a topographic representation of visual space
+
-
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How can we determine areas in the human?
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Tools for mapping human areas: function and topography
• Neuropsychological Lesions• Temporary Disruption
• transcranial magnetic stimulation (TMS)
• Electrical and magnetic signals• electroencephalography (EEG)
• magnetoencephalography (MEG)
• Brain Imaging• positron emission tomography (PET)
• functional magnetic resonance imaging (fMRI)
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Tools for mapping human areas:architectonics and connectivity• Human architectonics
– post-mortem analyses– high-resolution anatomical MRI
• Human connectivity– diffusion tensor imaging (DTI)– resting state connectivity– TMS-induced network changes
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How can we map human (visual) areas?
1. Look for homologues (or analogues) of known primate areas• Example: Human MT
2. Look for areas that may participate in highly enhanced human abilities• Example: Language, calculation, social interaction, tool use
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Back to our case study: MT
A patient with bilateral lesions to MT can no longer perceive motion (Zihl et al., 1983)
MT
V1
intermediate
A temporary disruption to human MT interferes with motion perception (Beckers & Zeki, 1995)
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fMRI of Human MT+ (V5+)
Moving vs. stationary dots activates V1 and MTFlickering vs. stationary checkerboards activates V1
Video: V1MTmovie.mpg
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Topography of Human MT+
21Huk, Dougherty & Heeger, 1002, J Neurosci
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Why put the plus in MT+?
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MT
MST
Dukelow et al., 2001, J Neurophysiol not shown: divisions of MST, FST
If you can’t distinguish the subdivisions, call it MT+
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Cytoarchitectonics of MT+
23Malicovik et al., 2007, Cereb Cortex
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Probabilistic Cytoarchitectonics
24Malicovik et al., 2007, Cereb Cortex
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DTI of MT+
25Lanyon et al., 2009, J Neuro-Ophthalmol
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Functional Connectivity of MT+
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Sani et al., 2011, Frontiers in Systems Neuroscience
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Evolutionary Relationships
expected locationactual location
Macaque: superior temporal sulcusHuman: inferior temporal sulcus
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Topographic Maps
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Macaque Retinotopy
Source: Tootell et al., 1982
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Distorted maps
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EXPANDINGRINGS
Retintopy: Flickering Checkerboard
• 8 Hz flicker (checks reverse contrast 8X/sec)• good stimulus for driving visual areas• subjects must maintain fixation (on red dot)
ROTATINGWEDGES
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time = 0
time = 20 sec
time = 60 sec
time = 40 sec
0 20 40 60
TIME
STIMULUSEXPECTED RESPONSE PROFILE OF AREA
RESPONDING TO STIMULUS
color code by phase of
peak response
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Retintopy: Eccentricity
calcarinesulcus
left occipitallobe
right occipitallobe
• foveal area represented at occipital pole• peripheral regions represented more anteriorly
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Retintopy on Flattened Occipital Lobe
2) cut along calcarinesulcus
left occipitallobe
3) unfold and flatten the cortical surface up
per
calc
arin
e su
lcus
low
er c
alca
rine
sulc
us
lateral surface (note: retinotopic areas do extend onto the lateral surface but are not shown here in this schematic)
1) virtually cut off the occipital lobe (remember, it’s a cup shape and the lateral surface is on the side we can’t see from this viewpoint)
occipital
pole
occipitalpole
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Retintopy: Eccentricity Movie
occipital pole
calcarine sulcus
Movie: eccentricity.mpeghttp://cogsci.ucsd.edu/~sereno/phasemovie2.mpg
Source: Marty Sereno’s web page
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Retintopy in V1: Polar Angle
calcarinesulcus
left occipitallobe
right occipitallobe
• left-right hemifields reverse (left field to right hemisphere)• upper-lower hemifields reverse (upper field to below calcarine)• horizontal meridian lies ~along calcarine (not always exactly)
HM
VM
VM
vertical meridian (VM)
horiz
onta
l mer
idia
n (H
M)
HM
VM
VM
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Polar Angle and Eccentricity in V1
calcarinesulcus
left occipitallobe
right occipitallobe
•retinotopic areas are like polar coordinates: eccentricity and polar angle
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Polar Angle in V1, V2 and beyond
left occipitallobe
• V2 is mirror image map of V1• V1-V2 border occurs at vertical meridian• V2-V3 border occurs at horizontal meridian• situation gets more complex in higher-tier areas (V4v, V3A) that have representations of whole hemifield
HM
VM
VM
vertical meridian (VM)
horiz
onta
l mer
idia
n (H
M)
} V1 lower
HM
} V2 lower
VM
} VP
} V1 upperHM
} V2 upperVM
} V3
calcarinesulcus
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Retinotopy
Source: Sereno et al., 1995
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Retinotopy: Polar Angle Movie
occipital pole
calcarine sulcus
Movie: phase.mpeghttp://zakros.ucsd.edu/~sereno/movies/phasemovie1b.mpg
Source: Marty Sereno’s web page
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Similarities Between Macaque and Human Maps
Tootell et al., 1996, Trends Neurosci.
MacaqueHuman(fMRI) (single
neurons)
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Getting Better Retinotopy
• use stimuli appropriate to the area (e.g., motion in MT+, color in V4v)• use stimuli that are attentionally engaging
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Other Sensory “-topies”
Touch: Somatotopy
Servos et al., 1998red = wrist; orange = shoulder
Audition: Tonotopy
cochlea
Sylvian fissure
temporal lobe
Movie: tonotopy.mpeghttp://cogsci.ucsd.edu/~sereno/downsweep2.mpg
Source: Marty Sereno’s web page
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Saccadotopy
Source: Sereno et al., 2001
•delayed saccades
•move saccadic target systematically around the clock
http://kamares.ucsd.edu/~sereno/LIP/both-closeup+stim.mpg
Marty Sereno’s web page
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There’s even maps in the frontal lobeIntraparietalSulcus(IPS)
LateralOccipital(LO)
VentralOccipital(VO)
Hagler & Sereno, 2006, NeuroImage
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Maps, Maps, Maps
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Important Points:1.Maps are everywhere (the better our techniqes, the more maps we find)2.Some maps represent ¼ of the visual field (e.g., lower left visual field in green-blue, as in V1); some maps represent ½ of the visual field (e.g., left visual field in red-green, e.g., IPS0); some maps represent whole visual field (yellow too)3.Regardless of ¼ vs. ½-field representation, maps are always mirror images that flip at the horizontal meridian (blue; solid line) or vertical meridian (red-green; dashed line)
Wandell et al., 2007, Neuron
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Foveal Confluences
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one foveal confluence
a separate foveal
confluenceWandell et al., 2007, Neuron
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Clustering of Areas
Wandell et al., 2007, Neuron
fovealrepresentation