Neuroscience & Behavior – Comprehensive Lecture II Notes

Central Nervous System (CNS) – Macro-Organization

• Three major divisions
  • Hindbrain (oldest evolutionary portion)
  • Medulla, pons, cerebellum, reticular formation
  • Relays/coordinates info with spinal cord; regulates basic life functions (breathing, heart rate, arousal)
  • Midbrain
  • Key relay for sensory ↔ motor processing
  • Tectum: orients organism to environment via sensory input (visual & auditory reflexes)
  • Tegmentum: supports movement, arousal; also contributes to orienting
  • Forebrain (largest in humans)
  • Cerebral cortex (lobes) + sub-cortical structures
  • Governs higher cognition (language, planning), emotion, advanced motor & sensory processing

Hindbrain – Detailed Structures

• Medulla: autonomic survival functions (respiration, circulation)
• Reticular Formation: sleep, wakefulness, arousal; filters incoming stimuli
• Cerebellum: fine motor coordination, balance, implicit motor learning
• Pons: bridges cortex ↔ cerebellum; regulates sleep cycles, respiration, facial expressions

Midbrain – Functional Highlights

• Acts like a central switchboard
• Supports reflexive orienting to novel sights/sounds (tectum)
• Assists basal ganglia with movement initiation (tegmentum)
• Dopaminergic nuclei in tegmentum contribute to reward & motivation

Forebrain – Cortex vs. Subcortex

• Cerebral Cortex (outer sheet)
  • Seat of complex cognition & conscious awareness
  • Highly folded to maximize surface area
  • Sulcus: valley; Gyrus: peak
• Subcortex (beneath cortex)
  • Thalamus: sensory relay/filter (all senses except smell)
  • Hypothalamus: homeostatic drives—temperature, hunger, thirst, sex; links nervous ↔ endocrine systems
  • Basal Ganglia: intentional movement selection & initiation
  • Hippocampus: formation & integration of new explicit memories; spatial navigation
  • Amygdala: emotion detection, regulation; tags memories with affective salience
  • Extensive hippocampus–amygdala interaction during emotional memory encoding

Grey Matter vs. White Matter

• Grey Matter: neuronal cell bodies, dendrites; minimal myelin ➔ local processing hubs
• White Matter: myelinated axon tracts; sparse cell bodies ➔ long-range communication
• Example: Corpus Callosum = massive white-matter tract connecting hemispheres

Associative Networks & Parallel Processing

• Brain rarely acts in isolated modules
• Parallel processing: multiple regions simultaneously handle different aspects of a task (e.g. reading involves vision, language, memory)
• Integration enabled by distributed networks of white-matter pathways

Inter-Hemispheric Communication

• Hemispheres separated by longitudinal fissure (deep sulcus)
• Corpus Callosum (white matter) = primary bridge; damage ➔ “split-brain” phenomena
• Degree of lateralization varies by function (language ⟶ typically left dominant)

Cortical Folding & Topography

• Folding increases cortical sheet area without enlarging skull
• Functional topographies:
  • Somatotopic maps in motor & somatosensory cortices (homunculi)
  • Close body parts represented by adjacent cortical zones
  • More cortical territory for areas with fine control/sensitivity (hands, lips)
• Contralateral organization: each hemisphere processes opposite body/visual field

Four Lobes of Each Hemisphere

1. Frontal Lobe
   • Primary motor cortex (posterior frontal gyrus)
   • Pre-motor & supplementary motor areas → movement planning
   • Broca’s area (left, inferior frontal) → speech production
   • Anterior prefrontal regions → executive control, personality, emotion regulation
2. Parietal Lobe
   • Somatosensory cortex: touch, proprioception
   • Integrates spatial info; guides attention & goal-directed actions
3. Occipital Lobe
   • Primary visual cortex (V1) receives retinal input → basic features
   • Visual processing streams radiate to secondary areas for color, motion, form
4. Temporal Lobe
   • Auditory cortex: sound processing (contralateral)
   • Wernicke’s area: language comprehension & construction
   • Ventral stream regions for object recognition; medial portions (hippocampus) for memory

Processing Gradient (Posterior → Anterior)

• Posterior sensory areas analyze raw input
• Mid-regions (parietal, temporal) combine features
• Anterior frontal areas generate abstract reasoning, volitional plans, decision-making

Language-Specific Cortical Areas

• Broca’s Area
  • Lesion → Broca’s (expressive) aphasia: non-fluent, effortful speech, relatively intact comprehension
• Wernicke’s Area
  • Lesion → Wernicke’s (receptive) aphasia: fluent but nonsensical speech, poor comprehension
• Both typically lateralized to left hemisphere

Neuroimaging – Windows into Structure & Function

Structural Imaging

• CT / CAT: X-ray slices; good for bleeds, bone; low resolution for soft tissue
• MRI
  • Uses strong magnetic field ➔ aligns atomic nuclei
  • Radio-frequency pulses knock nuclei; emitted energy differs by tissue ➔ high-resolution anatomy
• DTI
  • Variant of MRI; detects water diffusion along axons ➔ maps white-matter tracts

Functional Imaging / Electrophysiology

• EEG
  • Scalp electrodes detect summed postsynaptic potentials
  • High temporal (<$1$ ms), poor spatial resolution
• PET
  • Radioactive tracer (e.g. $\text{FDG}$) injected; gamma detectors measure metabolic activity
  • Good molecular specificity; limited temporal resolution (blood flow delay)
• fMRI
  • Sensitive to blood-oxygen-level–dependent (BOLD) signal (oxy- vs. deoxy-hemoglobin)
  • Measures hemodynamic response (~$4$–$6$ s lag)
  • High spatial (~$2$ mm) but indirect & slower than neuronal firing

Linking Damage to Function

• Natural lesions
  • Phineas Gage: iron rod pierced frontal lobes ➔ personality change, impulsivity ➔ role of frontal cortex in inhibition & emotion
  • Neurological diseases (Alzheimer’s, Parkinson’s, Pick’s, TBI) teach region–symptom relations
• Artificial lesions
  • Transcranial Magnetic Stimulation (TMS): transiently disrupts targeted cortical area; causally links region to function without permanent damage

Neuroplasticity – A Flexible Brain

• Neuroplasticity = brain’s capacity to reorganize structure/function
  • Functional plasticity: undamaged areas take over after injury (e.g. stroke recovery)
  • Structural plasticity: grey-matter volume & synaptic density change with skill learning (e.g. London taxi drivers’ enlarged hippocampi proportional to years on the job)
• Implication: rehabilitation & enrichment can harness plasticity for recovery/improvement

Split-Brain Phenomena (Corpus Callosotomy)

• Surgical severing of corpus callosum treats intractable epilepsy
• Hemispheres act together but cannot directly share info
  • Right visual field (RVF) → left occipital (language side) ➔ patient can verbally name objects
  • Left visual field (LVF) → right occipital ➔ patient cannot name but can select object with left hand
• Demonstrates lateralized specialization & need for inter-hemispheric integration
• Unique abilities: draw different shapes with each hand simultaneously

Hemispheric Specialization Overview

Note: Both hemispheres cooperate in most tasks; dominance ≠ exclusivity.

Clinical Reasoning Examples

• Pick’s Disease
  • Symptoms: speech issues, unusual behavior, hyperactivity, anxiety, lack of empathy
  • Suggests degeneration of frontal & temporal lobes (language + social/emotional regulation)
• Spinal Cord Injury Triage
  • Diminished abdominal reflexes imply damage near thoracic spinal segments (T8–T12)
  • Monitor autonomic organ control (e.g. bowel, bladder) governed by lower thoracic/lumbar pathways

Case Studies Mentioned

• Alzheimer’s Disease – progressive cortical atrophy, memory loss
• Parkinson’s Disease – substantia nigra degeneration; motor tremors
• Schizophrenia – disrupted dopaminergic pathways; hallucinations, delusions
• Traumatic Brain Injury (TBI) – diffuse axonal injury; varied cognitive/emotional deficits