Transcript Elevated Prevalence of left handedness in:

Elevated Prevalence of left
handedness in:
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Autism
Schizophrenia
Alcoholism
Criminals
Lawyers
Sleep difficulties
Stutterers
Immune disorders
• Math prodigies
• Gifted children
• Professional tennis &
baseball players
• Recent Presidents
• Architects
• Artists
Evolution of Handedness
• Nature vs Nuture
– Cultural mechanisms
– Environmental causes
– Genetic causes
Right-handedness
Other species?
Early humans?
Evidence from early humans
– Preferential wear on many cutting stone tools suggests
right handedness
– Art for 5,000 years of tool or weapon use
– 93% were right-handed when unimanual
– no systematic trends through time
» Few pieces prior to 3000 BC - Coren & Porac (1977)
– Hand outlines
• 70% are of the left hand
– Biblical evidence
• (Judges 20): 700 of 26,000 of children of Benjamin “restricted in
use of the right hand” = 2.7% left-handed
Causes of Left Handedness
• Environmental
– Early brain injury
• 7.3% in normal elementary schools vs
• 18.2 % in special education facilities (in 1920)
• 14-14.5 % in twins v 8.5 % in single births (in 1940)
– Cultural pressure for right handedness
• Genetic
– Right Shift Hypothesis
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Child’s handedness given parents’ handedness
R-R: 92.4%
R-L: 80.5%
L-L: 45.5 %
Left-Handedness Across the Life Span
• Proportion of left handers
drops with age
– 14% of 10-year-olds
– 5% of 50-year-olds
– < 1% of 80-year-olds
• Cause is unknown
– Longevity hypothesis
– Modification hypothesis
Curse or blessing of left-handedness
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Possible disadvantages
– Left-handers are 6x to die in accident
– 4x to die while driving
– More likely to have fingers amputated by
power-tools, suffer wrist fractures
– Lefties more susceptible to allergies, reading
disabilities, and migraines
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Possible advantages
– Lefties are more common among baseball &
tennis players, architects and artists
– Corpus callosum is 11% greater
• Possible greater integration of both brain
hemispheres in processing information
Brain areas involved in Language
Sensory-processing
contralateral pathways
Visual
Pathway
Lateralized Eye Movements
• Synonym for walking or intelligence
• Define impish or prudish
• Which direction does Thomas Jefferson
face on the nickel (west/left)
• Which states share a border with North
Carolina (VA, TN, SC)
Lateralized Eye Movements (LEM)
• Which way you look tells me (the
observer) which brain you activated?
– Leftward movement from my perspective
indicates LH activation
• (RVF squashed so LH will not be distracted when
doing the work)
– Rightward movement from my perspective
means RH is doing the work
Street Test of Right Hemisphere Dominance
Mooney (1957) – ID age & gender
Left hemisphere dominance
Similarities Test (selected items)
• Orange
• Banana
• Coat
• Dress
• Wagon
• Bicycle
• Wood
• Alcohol
• Egg
• Seed
• Poem
• Statue
• Fly
• Tree
Left Hemisphere
• Right hand touch and
movement
• Analytical processing
• Verbal skills
– Speech, writing
Right Hemisphere
• Left hand touch and
movement
• Holistic & Nonverbal
processing including
emotional tone and content
• Spatial processing
– Face recognition
Neuroimaging methods
• STRUCTURAL =density differences
– CT (Computerized Tomography)
– MRI (Magnetic resonance imaging)
• Combines slices for 3-D image
• FUNCTIONAL = electrical activity, blood flow, oxygenation
– EEG (Topography) 1929
• MEG (Magnetoencephalogram)
• TMS (Transcranial Magnetic Stimulation)
– PET (Positron Emission Tomography) 1970
• Measure of cerebral glucose level
• Advantages: high spatial resolution
• Disadvantages: somewhat invasive
– fMRI (functional MRI) 1990
Positron Emission Tomography
(PET) (blood flow)
Anatomical MRI
(T1-weighted)
Anatomical MRI
MRI
examples
(T2-weighted)
Functional MRI
(activation to music)
Structural MRI
(gray matter thickness map)
Diffusion Tensor MRI
(white matter tracts)
Noisy & Claustrophobic
Electroencephalography (EEG) – Brainwaves
Neuroimaging Spatiotemporal resolution
Optical
Imaging
Spatial Resolution (mm)
10
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6
MEG / EEG
PET
4
fMRI
2
MRI
Single / Multi
Unit Recording
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1 msec
1 sec
1 min
Temporal Resolution (sec)
10 min 1 hour