Note on sources: The library does not contain Stuart Ira Fox's Human Physiology or Sherwood's Human Physiology: From Cells to Systems as separate titles. The following comprehensive review is built from the best available physiology and neuroscience textbooks in the library — Guyton & Hall Textbook of Medical Physiology, Kaplan & Sadock's Comprehensive Textbook of Psychiatry, Neuroscience: Exploring the Brain (5th ed.), Neuroanatomy through Clinical Cases (3rd ed.), Adams and Victor's Principles of Neurology, and Katzung's Basic & Clinical Pharmacology. The content maps exactly to the topics Fox and Sherwood cover; citations to Fox/Sherwood are provided from textbook knowledge below the library content.

Emotional States, the Limbic System, and Higher Cortical Functions

1. Emotional States

• Where do emotions arise in the brain?
• How do they drive behavior and homeostasis?
• How are they disturbed in psychiatric disease?

• Emotions involve cortical (prefrontal, cingulate, insular) + subcortical (amygdala, hypothalamus, thalamus) integration.
• The hypothalamus translates emotional states into autonomic and hormonal responses (heart rate, blood pressure, stress hormones).
• The prefrontal cortex (PFC) regulates and modulates emotional intensity.
• Neurotransmitter systems — especially dopamine and serotonin — are key modulators.

2. The Limbic System

Historical Origin

Major Structures

Limbic Cortex Architecture

1. Orbitofrontal area (ventral frontal lobe)
2. Subcallosal gyrus
3. Cingulate gyrus (dorsal, follows corpus callosum)
4. Parahippocampal gyrus and uncus (ventromedial temporal lobe)

Subgenual Anterior Cingulate (Area 25) — Clinical Significance

Anatomy of the limbic system (Guyton & Hall, Fig. 59.4)

Key position of the hypothalamus in the limbic system (Guyton & Hall, Fig. 59.5)

3. The Amygdaloid Complex

Anatomy

• Ventral amygdalofugal pathway (diffuse, bilateral)
• Stria terminalis (arched tract following caudate nucleus)

Cross-section of the amygdala showing nuclear groups and connections (Neuroscience: Exploring the Brain, Fig. 18.14)

Klüver–Bucy Syndrome

• Visual agnosia — poor visual recognition despite intact vision
• Hyperorality — placing all objects in the mouth to explore them
• Hypersexuality — markedly increased sexual behavior
• Emotional blunting — dramatic loss of fear and aggression (e.g., a wild monkey lets humans approach freely)
• Dietary changes — altered food preferences

Amygdala and Fear

• Assigns emotional salience to stimuli (positive and negative)
• Coordinates the fear response (startle, autonomic activation, hormone release)
• Mediates fear conditioning (learning to associate a neutral stimulus with danger)
• Is involved in anxiety disorders and PTSD

4. Emotional Response — Neural Circuits

Papez Circuit (Hippocampal-Limbic Loop)

Hypothalamic Control of Emotional Expression

• Autonomic responses: heart rate, blood pressure, sweating, GI motility ("fight or flight")
• Endocrine responses: CRH → ACTH → cortisol (stress axis)
• Somatic responses: facial expression, vocalization, body posture

Prefrontal Cortex Role

5. The Dopaminergic System

6. Parkinson's Disease — Dopaminergic Basis

Pathophysiology

• Muscular rigidity (cogwheel or lead-pipe)
• Fine resting tremor ("pill-rolling")
• Shuffling gait (festinating)
• Bradykinesia (slowness of movement)
• Postural instability

Basal Ganglia Circuitry in PD

• Direct pathway: Striatum (substance P neurons) → GPi (inhibitory) → Thalamus disinhibited → Motor cortex activated (pro-movement)
• Indirect pathway: Striatum (enkephalin neurons) → GPe → STN → GPi → Thalamus inhibited → Motor cortex suppressed (anti-movement)

Treatment

Key clinical link: Typical antipsychotics (D2 blockers used in schizophrenia) frequently produce parkinsonian side effects by blocking nigrostriatal D2 receptors.

7. Schizophrenia — The Dopamine Hypothesis

Classic Dopamine Hypothesis

1. Most antipsychotics strongly block D2 receptors, especially in the mesolimbic/striatal system
2. Drugs that increase DA activity (levodopa, amphetamines, bromocriptine) aggravate or precipitate psychosis
3. Postmortem studies show increased D2-receptor density in untreated schizophrenics
4. Imaging shows increased amphetamine-induced striatal DA release and increased baseline D2 occupancy
5. Increased striatal dopamine synthesis and release found on PET

Negative Symptoms and Cognitive Impairment

• Negative symptoms: emotional blunting, social withdrawal, alogia, avolition
• Cognitive impairment: working memory deficits, executive dysfunction

Beyond Dopamine

• NMDA receptor hypofunction (glutamate hypothesis): PCP/ketamine (NMDA antagonists) reproduce both positive and negative symptoms, suggesting GABAergic interneuron dysfunction → disinhibited glutamate output
• This is now a leading research direction for new antipsychotic drug development

8. Cerebral Cortex — Structure and Associative Areas

Macro-architecture

• Pyramidal cells (~75% of neurons): excitatory, use glutamate; long-range projection neurons; have apical dendrites with dendritic spines (sites of excitatory synapses). In schizophrenia, dendritic spines on pyramidal neurons in DLPFC layer 3 are reduced — possibly from actin dysregulation or excessive microglial pruning.
• Stellate/nonpyramidal cells (~25%): mainly inhibitory interneurons using GABA; local circuit neurons; subtypes include chandelier cells (parvalbumin+, synapse on axon initial segments) and basket cells

Cortical Associative Areas

9. Motor and Sensory Areas of the Cerebral Cortex

Primary Motor Cortex

• Location: Precentral gyrus (Brodmann area 4), anterior to central sulcus
• Contains Betz cells (giant pyramidal neurons) that project directly via the corticospinal tract to spinal motor neurons
• Somatotopically organized — the motor homunculus maps body regions, with disproportionately large representation for hands, face, and lips
• Lesions cause contralateral spastic paralysis

Supplementary Motor Area (SMA) & Premotor Cortex

• Just anterior to primary motor cortex (area 6)
• Involved in motor planning, sequencing, bimanual coordination
• Lesions impair initiation and sequencing of complex movements, not basic strength

Primary Somatosensory Cortex

• Location: Postcentral gyrus (Brodmann areas 3, 1, 2)
• Receives somatosensory input from the ventrobasal thalamus
• Sensory homunculus — same principle as motor homunculus; large hand and face representations
• Lesions → contralateral sensory loss (touch, proprioception, pain)

Inputs to Motor Cortex

1. Somatosensory parietal cortex — subcortical fibers
2. Corpus callosum — from opposite hemisphere
3. Ventrobasal thalamic complex — cutaneous and joint/muscle signals
4. Ventrolateral and ventroanterior thalamic nuclei — cerebellar and basal ganglia signals for coordination
5. Intralaminar thalamic nuclei — general excitability control

Somatotopic Organization Throughout the Neuraxis

Motor and somatosensory cortical areas — lateral and medial views (Neuroanatomy through Clinical Cases, Fig. 6.1)

10. Visualizing the Brain — Neuroimaging

Findings in Emotion and Psychiatry

• Sadness → increased blood flow in thalamus and medial PFC; more specifically, left amygdala, hippocampal formation, parahippocampal gyrus
• Anticipatory anxiety → increased flow to anterior insular cortex
• Depression → most replicated finding: decreased anterior brain metabolism, particularly left-sided; decreased DLPFC activity; increased paralimbic (amygdala, subgenual cingulate) activity; abnormally increased default mode network (DMN) connectivity
• Mania → opposite pattern (increased left anterior metabolism relative to depression)

Key brain regions involved in affect and mood disorders imaged by PET (Kaplan & Sadock, Fig. 13.8–17)

• Increased amphetamine-induced striatal DA release
• Increased baseline D2 receptor occupancy
• Increased DA synthesis in striatum — confirming mesolimbic hyperdopaminergia in psychosis

11. Speech — Neural Organization

Lateralization

Broca's Area (Area 44–45)

• Located in the inferior frontal gyrus (pars opercularis and triangularis), left hemisphere
• Function: Motor programming of speech output — converts language representations into instructions for the larynx, lips, tongue
• Also contributes to syntax processing and grammar

Wernicke's Area (Area 22)

• Located in the posterior superior temporal gyrus, left hemisphere
• Function: Auditory language comprehension — transforms incoming sounds into meaningful words

The Wernicke–Geschwind Model

1. Auditory input → auditory cortex (Heschl's gyri)
2. → Wernicke's area: sounds understood as words
3. → Arcuate fasciculus (bundle of axons): carries word-based signals to Broca's area
4. → Broca's area: programs muscular movements for speech
5. → Primary motor cortex (face area): executes articulation

12. Aphasia

Broca's Aphasia (Motor / Non-fluent / Expressive Aphasia)

• Lesion: Left inferior frontal gyrus (Broca's area, Brodmann 44–45)
• Speech: Non-fluent, labored, telegraphic — content words preserved, function words (articles, pronouns) omitted
• Comprehension: Relatively intact
• Repetition: Impaired
• Agrammatism: Unable to construct grammatically correct sentences
• Anomia: Word-finding difficulty
• Associated deficit: Often right hemiparesis (face area of motor cortex nearby)
• Can say overlearned sequences (days of the week) more easily than spontaneous speech

Wernicke's Aphasia (Fluent / Receptive Aphasia)

• Lesion: Left posterior superior temporal gyrus (Wernicke's area, Brodmann 22)
• Speech: Fluent, rapid, well-articulated but meaningless — paraphasic errors (wrong sounds, wrong words in same category, neologisms)
• Comprehension: Severely impaired (cannot follow commands)
• Repetition: Impaired
• Patients often unaware their speech is abnormal

Conduction Aphasia

• Lesion: Arcuate fasciculus (+ often parietal cortex) — disconnects Broca's from Wernicke's area
• Speech: Fluent
• Comprehension: Good
• Repetition: Severely impaired — the hallmark deficit
• Wernicke predicted this syndrome from his model before it was clinically described

Global Aphasia

• Large left perisylvian lesion (Broca's + Wernicke's areas both damaged)
• All language functions severely impaired
• Usually associated with right hemiplegia

Transcortical Aphasias

• Lesions around (but sparing) Broca's and Wernicke's areas
• Repetition is preserved (the arcuate fasciculus is intact) — differentiating feature
• Motor transcortical: non-fluent, preserved repetition, lesion anterior/superior to Broca's
• Sensory transcortical: fluent, poor comprehension, preserved repetition, lesion posterior to Wernicke's

13. Reading and Writing Disorders

Alexia (Acquired Reading Disorder)

• Lesion: Left (dominant) occipital cortex + posterior corpus callosum (typically posterior cerebral artery infarct)
• The left occipital lesion blocks visual input from the right hemifield
• The callosal lesion prevents right visual cortex signals from reaching left language areas
• Result: Patient can write normally but cannot read — not even their own writing
• Can name letters spelled aloud; mild color anomia often present
• Right homianopia typically present
• Mechanism: disconnection syndrome

• Lesion: Dominant inferior parietal lobule, angular gyrus region
• Both reading and writing are impaired
• Aphasia may be absent or mild (dysnomia)
• Can occur with Gerstmann's syndrome

Agraphia (Acquired Writing Disorder)

• Part of most aphasic syndromes (writing impairment parallels the spoken language deficits)
• Pure agraphia without aphasia: lesion of inferior parietal lobule of dominant hemisphere
• Callosal agraphia: Left-hand agraphia from corpus callosum lesion (disconnects language from right motor cortex)
• Writing is particularly sensitive to diffuse encephalopathy (e.g., metabolic, toxic) — usually the first higher cognitive function to deteriorate

Dyslexia vs. Alexia

• Alexia = acquired reading disorder (from brain damage)
• Dyslexia = developmental reading disorder (not due to discrete lesion)

Gerstmann's Syndrome

1. Agraphia (writing disorder)
2. Acalculia (arithmetic impairment)
3. Right-left disorientation
4. Finger agnosia (cannot name individual fingers)

Summary Table