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-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) % 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-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 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 examples Anatomical 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) Spatial Resolution (mm) Neuroimaging Spatiotemporal resolution MEG / EEG Single / Multi Unit Recording PET Optical Imaging MRI fMRI