🧠 1. Two Hemispheres - One Brain?
Key Discovery (Marc Dax, 1836):
ALL speech-impaired stroke patients had LEFT hemisphere damage → None had right damage only!
🧠 LEFT Hemisphere
Dominant for:
- Language & speech 🗣️
- Reading & writing ✍️
- Math & logic 🔢
- Analytical thinking 📊
- Right side of body 🤚
🧠 RIGHT Hemisphere
Dominant for:
- Spatial skills 🗺️
- Face recognition 😊
- Music & art 🎵🎨
- Emotional expression 💖
- Left side of body 🤚
LEFT hemisphere = Language | RIGHT hemisphere = Spatial → But they WORK TOGETHER via Corpus Callosum!
🗣️ 2. Language Areas in the Brain
🗣️ BROCA'S AREA
Location: Left Frontal Lobe
Function: Speech PRODUCTION
Damage: Broca's Aphasia
Can understand but can't speak fluently
"Slow, effortful, telegraphic speech"
👂 WERNICKE'S AREA
Location: Left Temporal Lobe
Function: Speech COMPREHENSION
Damage: Wernicke's Aphasia
Can speak fluently but makes no sense
"Word salad" - fluent nonsense
Arcuate Fasciculus:
Bundle connecting Broca's ↔ Wernicke's → Damage = Conduction Aphasia (can't repeat words)
🚫 3. Types of Aphasia
| Type |
Speech |
Comprehension |
Repetition |
Damage Site |
| Broca's |
Non-fluent ❌ |
Good ✅ |
Poor ❌ |
Left frontal |
| Wernicke's |
Fluent ✅ |
Poor ❌ |
Poor ❌ |
Left temporal |
| Conduction |
Fluent ✅ |
Good ✅ |
Very Poor ❌ |
Arcuate fasciculus |
| Anomic |
Fluent ✅ |
Good ✅ |
Good ✅ |
Angular gyrus |
| Global |
Non-fluent ❌ |
Poor ❌ |
Poor ❌ |
Large left damage |
Anomic Aphasia Example - The Stapler:
Patient knows what it is, how to use it, but CAN'T NAME IT! Uses circumlocution (going roundabout)
✂️ 4. Split-Brain Studies (Sperry & Gazzaniga)
Commissurotomy:
Cutting Corpus Callosum → Hemispheres can't communicate → Used to treat severe epilepsy
Famous Experiments:
The HEART Experiment:
"HE" shown to left hemisphere | "ART" shown to right hemisphere
Asked verbally → Said "HE" | Asked to point → Picked "ART"
⇒ LEFT speaks, RIGHT knows but can't say!
Key Finding:
Right hemisphere CAN understand → Just can't SPEAK about it
Without Corpus Callosum → "Two separate minds" in one brain!
Split-brain patients seem normal in daily life → But careful tests reveal "two brains"!
🤚 5. Lateralization & Handedness
Handedness Rules:
Right-handed (90%) → LEFT hemisphere dominant
Left-handed (10%) → Usually RIGHT hemisphere dominant (but variable!)
Famous Left-Handers:
Leonardo da Vinci 🎨 | Michelangelo 🗿 | Napoleon 👑 | Alexander the Great ⚔️
Other Dominances:
Eye (telescope test) | Ear (phone test) | Foot (kicking test)
Assessed by: Harris Tests of Lateral Dominance
Face Asymmetry:
Left-left composite faces look MORE emotional → Right hemisphere handles expression intensity
💭 6. Memory Systems
Definitions:
Memory: Information stored due to experience
Learning: Acquisition of new memories
| Type |
Duration |
Capacity |
Example |
| Sensory |
Milliseconds |
Large |
Seeing a flash |
| Short-Term (STM) |
Seconds-minutes |
7±2 items |
Phone number |
| Long-Term (LTM) |
Permanent |
Unlimited |
Your childhood |
Long-Term Memory Types:
- Declarative (Explicit): Facts you can state → Semantic (facts) + Episodic (events)
- Procedural (Implicit): Skills you can do → Riding bike, typing
🧠 7. Brain Areas for Memory
| Structure |
Memory Role |
Damage Effect |
| 🌊 Hippocampus |
Converting STM → LTM |
Can't form NEW memories |
| 🔺 Amygdala |
Emotional memories |
No emotional learning |
| 🧠 Prefrontal Cortex |
Working memory |
Can't hold info while using |
| 🏀 Cerebellum |
Motor memories |
Can't learn motor skills |
| 🎯 Thalamus |
Memory relay |
Severe amnesia |
Hippocampus doesn't STORE memories → It TRANSFERS them to cortex for permanent storage!
👨 8. Famous Case: Patient H.M.
Background:
Henry Molaison → Severe epilepsy → Both hippocampi removed (1953)
Seizures stopped BUT → Couldn't form new memories!
H.M.'s Deficits:
- ❌ Anterograde Amnesia: Couldn't form NEW declarative memories
- ❌ Forgot people he met minutes ago
- ❌ Read same magazine as "new" every time
- ✅ Preserved: Old memories (before surgery)
- ✅ Preserved: Procedural learning (could learn skills!)
Mirror Drawing Task:
H.M. improved at tracing in mirror each day → But NO memory of doing the task before!
⇒ Proved: Different memory systems exist!
🚫 9. Types of Amnesia
⏩ Anterograde
Can't form NEW memories
Past memories intact
Like H.M.
Hippocampus damage
⏪ Retrograde
Can't recall OLD memories
Can form new ones
Common after head injury
Often temporary
Korsakoff's Syndrome:
Caused by: Chronic alcoholism + thiamine deficiency
Results in: Both anterograde AND retrograde amnesia + confabulation (making up stories)
🔬 10. Lashley's Memory Research
Lashley's Frustration:
"I sometimes feel... that the necessary conclusion is that learning is just not possible" 😤
→ Searched whole life for "engram" (memory trace) - never found specific location!
His Two Principles:
1. Equipotentiality:
All parts of cortex contribute equally to memory → No single part is "special"
2. Mass Action:
Memory loss depends on AMOUNT of cortex damaged, not LOCATION
More cortex removed = More memory lost
Modern view: Lashley was partly right - memories ARE distributed, but some areas ARE more important!
🚫 11. Other Higher Function Disorders
Apraxia (Motor Disorders):
Definition: Can't perform learned movements despite having ability
Types:
- Ideomotor: Can't pantomime (show me how to use scissors)
- Ideational: Can't sequence actions (make tea)
- Constructional: Can't draw or assemble
Agnosia (Recognition Disorders):
Definition: Can't recognize despite intact senses
Types:
- Visual Agnosia: Can see but can't recognize objects
- Prosopagnosia: Can't recognize FACES (even family!)
- Auditory Agnosia: Can hear but can't identify sounds
- Amusia: Can't recognize music/tones
📖 12. Dyslexia
Definition: Difficulty reading/writing despite normal intelligence
Interesting Cultural Differences:
- English: More dyslexia (sound-based language)
- Chinese: Less dyslexia (visual symbols)
- Japanese: Kana (sound) affected, Kanji (visual) preserved!
Types:
Alexia with Agraphia: Can't read OR write (angular gyrus damage)
Pure Alexia: Can write but can't read own writing! ("Word blindness")
🔄 13. Brain Plasticity
Definition:
Brain's ability to reorganize, form new connections, compensate for damage
Evidence:
- Violin players → Larger finger areas in cortex
- London taxi drivers → Larger hippocampus
- Children recover from brain damage better than adults
- Blind people → Visual cortex repurposed for Braille/hearing
Hebb's Rule:
"Neurons that fire together, wire together" → Repeated use strengthens connections
Brain is NOT fixed! It changes throughout life based on experience and use!
📋 14. Neuropsychological Tests
| Test |
What It Tests |
| WADA Test |
Which hemisphere is dominant for language (inject barbiturate into one side) |
| Dichotic Listening |
Ear advantage for language (different sounds to each ear) |
| Visual Field Tests |
Which hemisphere processes what (show to one visual field) |
| Token Test |
Language comprehension |
| Boston Naming Test |
Word finding ability |
⚡ QUICK EXAM CHECKLIST
- ✅ Left vs Right hemisphere functions
- ✅ Broca's vs Wernicke's area and aphasia
- ✅ All types of aphasia and their features
- ✅ Split-brain studies and findings
- ✅ Memory types (STM, LTM, Declarative, Procedural)
- ✅ Brain areas for memory (Hippocampus especially!)
- ✅ H.M. case and what it taught us
- ✅ Anterograde vs Retrograde amnesia
- ✅ Lashley's two principles
- ✅ Apraxia vs Agnosia types
- ✅ Dyslexia and cultural differences
- ✅ Brain plasticity concept