Biological Processes

The Nervous System

Underlying Questions

• What is the relation between the mind and the brain?
• What is the physical basis of experience?
• To what extent is behavior learned and to what extent is it inherited?
• How and why did the human brain get so big?

Brief History of Mind-Brain Problem

• René Descartes (1596-1650)
• Body is a complex machine; mind is separate from the body.
• They communicate via the pineal gland.
• Non-human animals are unconscious automata.
• Some historians now wonder whether Descartes might have saved the soul to save himself.
• Led to "Cartesian Impasse."

Responses to Cartesian Impasse

• Nicolas Malebranche (1638-1715)
• Occasionalism: God is the only true cause; no influence of mind on body or body on mind.
• Gottfried Wilhelm Leibniz (1646-1716)
• Psychophysical parallelism: Mind & body are different entities, existing in perfect synchrony.

Responses to Cartesian Impasse

• George Berkeley (1685-1753)
• Immaterialism: Nothing exists independent of mind.
• Julien Offray de la Mettrie (1709-1751)
• Materialism: Nothing exists independent of matter. Conscious acts are distinguished from unconscious processes only by the relatively complexity of their physiology.

Turmoil in 19th Century

• Mind-brain problem especially acute in 19th Century
• Increasing understanding of localization of function in the nervous system.
  • Paul Broca; David Ferrier.
• Awareness that mental events bring about changes to the body/brain.
  • Hypnosis (Marquis de Puységur); mental illness.

19th Century Solutions

• Shadworth Holloway Hodgson (1832-1912)
• Epiphenomenalism: Mental states are produced by the brain but cannot affect the brain.
• William Benjamin Carpenter (1813-1885)
• Interactionism: Mind & brain are different but mutually interactive.
• George Henry Lewes (1817- 1878)
• Neutral monism: One kind of "stuff"; mind & brain differ in arrangement of stuff or perspective from which it is viewed.

What's the right answer?

• Uniform agreement that consciousness is produced by brains, & that the complexity of consciousness is correlated with the complexity of the brain.
• Uniform ignorance about how this happens.

Two Current Theories

• Consciousness is produced by a special class of neurons. Research should focus on identifying which neurons are correlated with consciousness and which are not.
• Consciousness is an irreducible phenomenon, like space, time, & gravity. To explain consciousness, we need new physical laws.

Nervous System

• Central Nervous System
• Brain & spinal cord
• Peripheral Nervous System
• Somatic: Sensory & motor nerves; voluntary
• Autonomic: Involuntary
  • Parasympathetic: storing energy, "calming."
  • Sympathetic: consuming energy, "arousing."

The Brain: Structure & Function

• Forebrain
• Midbrain
• Hindbrain

Forebrain

• Cerebral cortex: Sensation, perception, cognition, language, movement, etc.
• Limbic system (hippocampus, amygdala, septum): Learning, emotions, motivation.
• Thalamus (e.g., lateral geniculate nucleus): Sensory relay station.
• Hypothalamus: Controls endocrine system, autonomic nervous system; four Fs (feeding, fighting, fleeing, and mating).

Midbrain

• Superior colliculus: Involved in vision.
• Inferior colliculus: Involved in hearing.
• Substantia nigra: Releases dopamine.

Hindbrain

• Medulla & pons: Control of heart rate, breathing, vomiting, sneezing, etc.
• Reticular formation (also in midbrain): Consciousness (sleep & arousal), attention.
• Cerebellum: Planning and coordination of complex movements, cognition (?).

Cerebral Cortex

• Cerebral cortex: 2 mm thick layer on surface of brain; accounts for 80% of volume; "gray matter" (vs. "white matter").
• Two hemispheres: LH controls right side of body; RH controls left side of body.
• Hemispheres communicate via corpus callosum.

Example of Lateralization: Vision

Hemispheric Specialization

• Left hemisphere: Language.
• Right hemisphere: Spatial (?).
• Evidence: Brain damage (e.g., Paul Broca); "split-brain" patients.
• Lateralization can be used to study hemispheric specialization.

Split Brains

• Corpus callosum severed to treat epilepsy.
• Most behavior is normal.
• Object shown in the right visual field could be easily named; object shown in the left visual field seemed to be unrecognized.
• But it could be pointed to by the left but not the right hand!

 

Lobes of the Cerebral Hemispheres

• Frontal: Abstract reasoning, motor cortex.
• Parietal: Somatosensory processing.
• Temporal: Auditory processing.
• Occipital: Visual processing.

Example: Motor & Somatosensory Cortex

• Homunculus of the motor cortex (frontal).
• Homunculus of the somatosensory cortex (parietal).
• Principle: Topographic organization.

Summary

• Scientists still do not understand how brains produce consciousness.
• Different areas of the nervous system do different things: CNS vs. PNS; hemispheric specialization; localization of function.
• Information processing is accomplished in neurons, which communicate via neurotransmitters.