Transcript Brain Areas and Topography

Jody Culham
Brain and Mind Institute
Department of Psychology
University of Western Ontario
http://www.fmri4newbies.com/
Brain Areas and Topography
Last Update: January 2011
Last Course: Psychology 9224, W2011, University of Western Ontario
What Defines an Area?
2
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
3
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)
4
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
7
Brodmann Area 17 Meets 21st Century
Anatomical MRI
Logothetis fMRI data:
image from http://www.bruker-biospin.com/imaging_neuroanatomy.html
Functional MRI
Goense, Zappe & Logothetis, 2007, MRI
Layer 4 fMRI activation (0.3 x 0.3 x 2 mm spin echo)
8
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
9
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
10
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
11
MT Architecture
• MT is stained with cytochrome
oxidase (which indicates high
metabolic activity)
12
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
13
MT Topography
• MT has a topographic representation of
visual space
+
-
14
How can we determine areas in the
human?
15
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)
16
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
17
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
18
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)
19
fMRI of Human MT+ (V5+)
Video: V1MTmovie.mpg
Moving vs. stationary dots activates V1 and MT
Flickering vs. stationary checkerboards activates V1
20
Topography of Human MT+
Huk, Dougherty & Heeger, 1002, J Neurosci
21
Why put the plus in MT+?
MT
MST
Dukelow et al., 2001, J Neurophysiol
not shown: divisions of MST, FST
If you can’t distinguish the subdivisions, call it MT+
22
Cytoarchitectonics of MT+
Malicovik et al., 2007, Cereb Cortex
23
Probabilistic Cytoarchitectonics
Malicovik et al., 2007, Cereb Cortex
24
DTI of MT+
Lanyon et al., 2009, J Neuro-Ophthalmol
25
Functional Connectivity of MT+
Sani et al., 2011, Frontiers in Systems Neuroscience
26
Evolutionary Relationships
expected location
actual location
Macaque: superior temporal sulcus
Human: inferior temporal sulcus
27
Topographic Maps
Macaque Retinotopy
Source: Tootell et al., 1982
Distorted maps
30
Retintopy: Flickering Checkerboard
EXPANDING
RINGS
ROTATING
WEDGES
• 8 Hz flicker (checks reverse contrast 8X/sec)
• good stimulus for driving visual areas
• subjects must maintain fixation (on red dot)
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
time = 60 sec
20
40
TIME 
60
Retintopy: Eccentricity
calcarine
sulcus
left occipital
lobe
• foveal area represented at occipital pole
• peripheral regions represented more anteriorly
right occipital
lobe
Retintopy on Flattened Occipital Lobe
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
2) cut along calcarine
sulcus
left occipital
lobe
3) unfold and flatten
the cortical surface
lateral surface
(note: retinotopic
areas do extend
onto the lateral
surface but are not
shown here in this
schematic)
occip
ital
pole
Retintopy: Eccentricity Movie
calcarine sulcus
occipital pole
Movie: eccentricity.mpeg
http://cogsci.ucsd.edu/~sereno/phasemovie2.mpg
Source: Marty Sereno’s web page
horizontal meridian (HM)
Retintopy in V1: Polar Angle
calcarine
sulcus
VM
VM
HM
HM
VM
vertical meridian (VM)
VM
left occipital
lobe
right occipital
lobe
• 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)
Polar Angle and Eccentricity in V1
calcarine
sulcus
left occipital
lobe
right occipital
lobe
•retinotopic areas are like polar coordinates: eccentricity and polar angle
horizontal meridian (HM)
Polar Angle in V1, V2 and beyond
VM
calcarine
sulcus
HM
VM
HM
VM
HM
vertical meridian (VM)
VM
left occipital
lobe
• 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
Retinotopy
Source: Sereno et al., 1995
Retinotopy: Polar Angle Movie
calcarine sulcus
occipital pole
Movie: phase.mpeg
http://zakros.ucsd.edu/~sereno/movies/phasemovie1b.mpg
Source: Marty Sereno’s web page
Similarities Between Macaque and Human Maps
Human
Macaque
(fMRI)
(single
neurons)
Tootell et al., 1996, Trends Neurosci.
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., 1998
red = wrist; orange = shoulder
Audition:
Tonotopy
Sylvian fissure
temporal lobe
cochlea
Movie: tonotopy.mpeg
http://cogsci.ucsd.edu/~sereno/downsweep2.mpg
Source: Marty Sereno’s web page
Saccadotopy
•delayed saccades
•move saccadic target
systematically around the
clock
Source: Sereno et
al., 2001
http://kamares.ucsd.edu/~sereno/LIP/both-
There’s even maps in the frontal lobe
Intraparietal
Sulcus
(IPS)
Lateral
Occipital
(LO)
Hagler & Sereno, 2006, NeuroImage
Ventral
Occipital
(VO)
Maps, Maps, Maps
Wandell et al., 2007, Neuron
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)
46
Foveal Confluences
one foveal
confluence
Wandell et al., 2007, Neuron
a separate
foveal
confluence
47
Clustering of Areas
foveal
representation
Wandell et al., 2007, Neuron