Brain Areas and Topography

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Brain Areas and Topography
Jody Culham Brain and Mind Institute Department
of Psychology University of Western Ontario
http//www.fmri4newbies.com/
Last Update January 2011 Last Course
Psychology 9224, W2011, University of Western
Ontario
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What Defines an Area?
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Definition of an Area

• Neuroimagers 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
• Neuroanatomists 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

• Function
• an area has a unique pattern of responses to
  different stimuli
• Architecture
• different brain areas show differences between
  cortical properties (e.g., thickness of different
  layers, sensitivity to various dyes)
• Connectivity
• Different areas have different patterns of
  connections with other areas
• 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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Brodmanns Areas
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Brodmann Area 17
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Brodmann Area 17 Meets 21st Century
Anatomical MRI
Functional MRI
Layer 4
Logothetis fMRI data image from
http//www.bruker-biospin.com/imaging_neuroanatomy
.html
Goense, Zappe Logothetis, 2007, MRI Layer 4
fMRI activation (0.3 x 0.3 x 2 mm spin echo)
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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 Function

• Single 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 areasarchitectonics 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?

• Look for homologues (or analogues) of known
  primate areas
• Example Human MT
• 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
MT
intermediate
V1
A patient with bilateral lesions to MT can no
longer perceive motion (Zihl et al., 1983)
A temporary disruption to human MT interferes
with motion perception (Beckers Zeki, 1995)
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fMRI of Human MT (V5)
Video V1MTmovie.mpg
Moving vs. stationary dots activates V1 and
MT Flickering vs. stationary checkerboards
activates V1
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Topography of Human MT
Huk, Dougherty Heeger, 1002, J Neurosci
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Why put the plus in MT?
MT
MST
Dukelow et al., 2001, J Neurophysiol
not shown divisions of MST, FST
If you cant distinguish the subdivisions, call
it MT
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Cytoarchitectonics of MT
Malicovik et al., 2007, Cereb Cortex
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Probabilistic Cytoarchitectonics
Malicovik et al., 2007, Cereb Cortex
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DTI of MT
Lanyon et al., 2009, J Neuro-Ophthalmol
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Functional Connectivity of MT
Sani et al., 2011, Frontiers in Systems
Neuroscience
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Evolutionary Relationships
expected location
actual location
Macaque superior temporal sulcus Human 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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Retintopy Flickering Checkerboard

• 8 Hz flicker (checks reverse contrast 8X/sec)
• good stimulus for driving visual areas
• subjects must maintain fixation (on red dot)

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EXPECTED RESPONSE PROFILE OF AREA RESPONDING TO
STIMULUS
STIMULUS
time 0
color code by phase of peak response
time 20 sec
time 40 sec
0
20
40
60
TIME ?
time 60 sec
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Retintopy Eccentricity
calcarine sulcus
left occipital lobe
right occipital lobe

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

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Retintopy on Flattened Occipital Lobe
1) virtually cut off the occipital lobe
(remember, its a cup shape and the lateral
surface is on the side we cant see from this
viewpoint)
occipital pole
2) cut along calcarine sulcus
upper calcarine sulcus
lateral surface (note retinotopic areas do
extend onto the lateral surface but are not shown
here in this schematic)
3) unfold and flatten the cortical surface
occipital pole
left occipital lobe
lower calcarine sulcus
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Retintopy Eccentricity Movie
calcarine sulcus
occipital pole
Movie eccentricity.mpeg http//cogsci.ucsd.edu/s
ereno/phasemovie2.mpg Source Marty Serenos web
page
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Retintopy in V1 Polar Angle
calcarine sulcus
horizontal meridian (HM)
VM
VM
HM
HM
VM
VM
left occipital lobe
right occipital lobe
vertical meridian (VM)

• 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)

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Polar Angle and Eccentricity in V1
calcarine sulcus
left occipital lobe
right occipital lobe

• retinotopic areas are like polar coordinates
  eccentricity and polar angle

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Polar Angle in V1, V2 and beyond
calcarine sulcus
V1 upper
horizontal meridian (HM)
V1 lower
VM
HM
VM
left occipital lobe
vertical meridian (VM)

• 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

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Retinotopy
Source Sereno et al., 1995
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Retinotopy Polar Angle Movie
calcarine sulcus
occipital pole
Movie phase.mpeg http//zakros.ucsd.edu/sereno/m
ovies/phasemovie1b.mpg Source Marty Serenos web
page
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Similarities Between Macaque and Human Maps
Macaque
Human
(single neurons)
(fMRI)
Tootell et al., 1996, Trends Neurosci.
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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., 1998 red wrist orange shoulder
Audition Tonotopy
Sylvian fissure
temporal lobe
cochlea
Movie tonotopy.mpeg http//cogsci.ucsd.edu/seren
o/downsweep2.mpg Source Marty Serenos web page
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Saccadotopy

• delayed saccades
• move saccadic target systematically around the
  clock

Source Sereno et al., 2001
http//kamares.ucsd.edu/sereno/LIP/both-closeups
tim.mpg Marty Serenos web page
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Theres even maps in the frontal lobe
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Maps, Maps, Maps

• Important Points
• Maps are everywhere (the better our techniqes,
  the more maps we find)
• 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)
• 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
one foveal confluence
a separate foveal confluence
Wandell et al., 2007, Neuron
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Clustering of Areas
foveal representation
Wandell et al., 2007, Neuron