Elevated Prevalence of left handedness in:

• 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-handednessOther 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

• 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

• 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

• 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-processingcontralateral 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

• Coat

• Wagon

• Wood

• Egg

• Poem

• Fly

• Banana

• Dress

• Bicycle

• Alcohol

• Seed

• Statue

• 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)

MRI examplesAnatomical MRI(T1-weighted)

Structural MRI(gray matter thickness map)

Anatomical MRI(T2-weighted)

Functional MRI(activation to music)

Diffusion Tensor MRI(white matter tracts)

Noisy & Claustrophobic

Electroencephalography (EEG) – Brainwaves

1 msec 1 sec 1 min 10 min 1 hour

Temporal Resolution (sec)

Sp

atia

l Res

olu

tio

n (

mm

)

10

8

6

4

2

0

Neuroimaging Spatiotemporal resolutionNeuroimaging Spatiotemporal resolution

MEG / EEG

Single / Multi Unit Recording

PET

OpticalImaging

MRI

fMRI