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?

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)

Macaque Visual Maps

• Over 30 visual areas

• Visual areas make up ~40% of monkey brain

Van Essen et al., 2001

Brodmann’s Areas

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

Topography of Human MT+

21Huk, Dougherty & Heeger, 1002, J Neurosci

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+

Cytoarchitectonics of MT+

23Malicovik et al., 2007, Cereb Cortex

Probabilistic Cytoarchitectonics

24Malicovik et al., 2007, Cereb Cortex

DTI of MT+

25Lanyon et al., 2009, J Neuro-Ophthalmol

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

Topographic Maps

Macaque Retinotopy

Source: Tootell et al., 1982

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

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

Retintopy: Eccentricity

calcarinesulcus

left occipitallobe

right occipitallobe

• foveal area represented at occipital pole• peripheral regions represented more anteriorly

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

Retintopy: Eccentricity Movie

occipital pole

calcarine sulcus

Movie: eccentricity.mpeghttp://cogsci.ucsd.edu/~sereno/phasemovie2.mpg

Source: Marty Sereno’s web page

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

Polar Angle and Eccentricity in V1

calcarinesulcus

left occipitallobe

right occipitallobe

•retinotopic areas are like polar coordinates: eccentricity and polar angle

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

Retinotopy

Source: Sereno et al., 1995

Retinotopy: Polar Angle Movie

occipital pole

calcarine sulcus

Movie: phase.mpeghttp://zakros.ucsd.edu/~sereno/movies/phasemovie1b.mpg

Source: Marty Sereno’s web page

Similarities Between Macaque and Human Maps

Tootell et al., 1996, Trends Neurosci.

MacaqueHuman(fMRI) (single

neurons)

Getting Better Retinotopy

• use stimuli appropriate to the area (e.g., motion in MT+, color in V4v)• use stimuli that are attentionally engaging

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

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

There’s even maps in the frontal lobeIntraparietalSulcus(IPS)

LateralOccipital(LO)

VentralOccipital(VO)

Hagler & Sereno, 2006, NeuroImage

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

Foveal Confluences

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one foveal confluence

a separate foveal

confluenceWandell et al., 2007, Neuron

Clustering of Areas

Wandell et al., 2007, Neuron

fovealrepresentation