Neurocognition & Brain Imaging – Key Vocabulary

Neural Portrait of the Human Mind – Key Take-Aways

Dr. Nancy Kanwisher’s TED Talk (Context)

• Builds on earlier debate between:
  • Carl Lashley’s equipotentiality / distributed-network view (all cortical tissue can do all cognitive jobs).
  • Modern localization of function view (distinct cortical modules for distinct computations).
• Kanwisher’s functional-MRI (fMRI) findings: demonstrates discrete cortical patches that respond preferentially to specific stimulus classes (faces, places, bodies, words, etc.).
• Central caution: All imaging evidence is correlational. Activation ≠ proof of necessity or causality.

Localization vs. Distribution

• Contemporary consensus:
  • Yes, cognitive operations are localized, yet
  • Modules operate inside interconnected networks (no island-like isolation).
• Example chain:
  • Memory ≠ a single spot → relies on hippocampus + cortical association areas + amygdala, etc.
  • Language involves Broca’s (speech production) + Wernicke’s (speech comprehension) + arcuate fasciculus.

Why “Correlational”?

Methods & Caveats

• Post-mortem lesion analysis – identifies destroyed tissue after known behavioral loss (e.g., Broca’s original cases).
• EEG – tracks millisecond-level electrical oscillations; excellent temporal, poor spatial resolution.
• PET – radioactive glucose uptake; indexes metabolic demand.
• Structural MRI – high-resolution anatomy snapshot.
• Functional MRI (fMRI)
  • Measures BOLD signal (Blood-Oxygen-Level Dependent); proxy for neural activity via local blood-flow changes.
  • Brain ≈ muscle: greater metabolic use → greater \text{O}_2 & glucose → measurable signal.
  • Subtractive design: alternate “Task ON” vs. “Task OFF” blocks, subtract baseline to isolate task-specific voxels (e.g., view face vs. view scrambled patterns).
• Because none directly stimulate/destroy tissue (except rare electrode studies), causal claims require caution.

The Fusiform Face Area (FFA)

• Location: right fusiform gyrus, ~2 inches medial, 1.5 inches inferior to lateral surface.
• Function: high-level, holistic face recognition.
• Evidence lines:
  • fMRI shows selective BOLD spikes to faces.
  • Electrode stimulation (Kanwisher clip) in epilepsy surgery: subject’s report “your face just metamorphosed.” (Causal link!)
  • Lesion data → prosopagnosia when FFA compromised.
• Neuroplasticity anecdote: dairy farmer repurposed FFA for cow-face expertise → cortical territory can be functionally reassigned by long-term experience.

Prosopagnosia – “Sensation Without Perception”

• Damage → intact low-level vision (eyes, retina, V1, etc.) but cannot integrate facial features into a recognizable identity.
• Demonstrates bottom-up vs. top-down split:
  • Bottom-up (sensation) = physical energy → neural code.
  • Top-down (perception) = interpretation, meaning, holistic recognition.
• Hence dubbed “face blindness.” Sufferers rely on voice, gait, clothing, or contextual cues for identification.

Key Brain Areas Mentioned

• Broca’s area – frontal lobe, speech production.
• Wernicke’s area – superior temporal gyrus, language comprehension.
• Primary motor cortex – precentral gyrus; voluntary movement.
• Primary visual cortex (V1) – occipital pole; early visual processing.
• Hippocampus – medial-temporal, episodic memory consolidation.

Broader Implications & Connections

• Ethical / interpretive: avoiding reverse inference (“area lit up → you must be doing X”).
• Clinical relevance:
  • Mapping eloquent cortex before neurosurgery (tumor/epilepsy) to spare vital functions.
  • Rehabilitation strategies leverage neuroplasticity (future lecture) to retrain lost functions.
• Philosophical: The mind cannot be pinned to a single lump of tissue, yet neither is it an undifferentiated soup; cognition arises from specialized, networked substrates.