Neuroscience: Historical Perspectives
Early Theories: Mind/soul - Body/Brain
Localise Mind without Brain: Neuroanatomy
Neuron Doctrine: Modern Neuroscience
Localisation and Brain Mapping: Phrenology to Cortical Topography
Mind brain - related but separate, Magnus: brain = centre of mental activity, mental brain and function = linked but mind is immaterial
Plato
Earliest = Egyptians
- Cases of head/neck injuries
- Brain controlling behaviour
- Heart is most important (mummification)
Homer - Psyche: non-localised soul, individual life/identity, NOT specific body part, dreams (prior to Freud), life vs body soul
Natural Philosophers
Explain constitution of matter in substances (elements)
Rejected supernatural
Addressed problem of nature of soul
Brain or heart?
Encephalocentrism: brain is seat of human consciousness, sensation and knowledge
Cardiocentrism: attributed all these faculties to the heart
Anatomical dissections
Western Medicine
Aristotle - Cardiocentric, different soul faculties, reside in heart
Galen
Cognitive sig. of brain - channel like structure
Human brain similar to animals (2 hemispheres)
Seat of consciousness and sensation
Distinguished bewteen sensation and understanding (build on)
Lateralisation of effects of brain injury
Epilepsy not scared
Brain = seat of intellect, causing neurological disorders
no difference between sense in the brain, more central functions (Sensation + knowledge)
Encephalicentric
3 species of soul
- Logos (head/divine)
- Thymos (chest/feelings)
- Epithemtikon (liver/hunger, passion, unconsious)
Against cardio-centric
Brain received sensations, produces images and understands thoughts
Rigorous anatomical testing
Brain + spine = nerves (connections)
Ventricular Hypothesis
Pig = kept breathing, not squealing, after throat nerves cut - voice from brain not heart
Brain = reciprocal for the soul - communication
Neuroanatomy rebirth
Da Vinci - relating structure to mental function
Anatomical detail
Wax cast of ventricle
Ventricularist - responsible for major brain functions, soul in brain rather than surrounding
Vesalius = Non-ventricularist
Rejected ventricular localisation
Mammals = same brain but not intelligence
Cartesian Legacy
Mediated by fluid dynamics
Tech as metaphor
"Balloonist Theory": brain controlled body mechanically via fluids
Mind in pineal gland (endocrine gland) - between two hemispheres
Cartesian Dualism = immaterial and material interaction
Gap = how can they interact?
Cortex = seat of psychological functions
- Still cartesian - so still problem with gap
- contact and causal interaction is cortex not pineal gland
Understanding nervous system
Microscopy > understanding of nervous system organisation
Histological methods > detail
Reticularists vs. Cell theories
Dendrites, cell bodies, axons
R = NS is large network of tissue, fused processes. Network not individual cells
CT = cells are separate but communicate as NS
Both = same methods but different conc. about structure
Limit = low mag + poor resolution
Organisation of NS
Purkinje Cells
Golgi Staining
Modern Neuroscience
Rete Nervosa Diffusa
Early microscopes = distortions, Newer = clearer
Discovering cerebellar cells (largest invertebrate)
Microscopic image of nerve
Silver nitrate method
Nervous tissue = continuous, not discrete
Connections with infinite others
Holistic approach: NS as reticulum
Thought observation confirmed hyp that NS = continuous network
Santiago, Ramon and Cajal
Acceptance of Neuron Doctrine
Neuron = anatomical/functional unit of NS
Relationship is not continuity but contiguity
Staining Improved - Cajal
Neuron
Tenets
- Fundamental structural and functional unit of NS is neuron
- Neurons = discrete not continuous cells
- 3 Parts - dendrites, cell body, axon
- Info flows in one direction
Reasons for delay
- Technical: histological preparation and optic quality microscope need to be improved
- Area of study: nerve cells = extraordinary complex + variable structure
- Theoretical: Belief that cell continuity necessary for interaction
Immersing tissues in fixative and silver nitrate 2nd, deep
Axon endings = consistent with location of dendrites
No evidence for reticulum - abandoned
Constituted by numerous neuron units
Nerve cell, nerve fibre, terminal arborizations
Synapse = direction (polarised)
Theory supported by electron microscope techniques
Early Observation Effects of Brain Damage - Diseases of the brain, not paralysed tongue but can't speak > memory
Localisation
Phrenology
Against Localization
Brain Mapping + Lesions
Wernicke's Aphasia
Brain equipotentiality theory: brain functions as whole
Localisation: specialisation in the brain
- Brain composed of many organs, dedicated to particular skill
- Size of organ = measure of power
- Shape = determined by development of organs
- Skull takes shape from brain > surface = accurate index
*Greater use = increased - Analysis = insight into personality
Phrenometer = measure bumps on skulls
Functional specialisation = not empirically derived/constrained by theories
Animal lesions did not cause specific deficits
Aggregate field: whole brain in behaviour
One faculty, one seat in organs
Cortical specialisation for uniquely human capacity for speech
Lost speech 20yrs before
Post-mortem
Lesion in L inferior frontal cortex
Specific area and specific dysfunction
Language understanding
Problems after damage to posterior part of L hemisphere
Nothing to do with speaking but understanding
Brain Mapping
First
Motor Cortex
Dogs stimulated with electric current
W/ Anatomy
Contribution
Surface = muscles contractions face and neck on opposite side
Unilateral ablation of forepaw did not affect sensation but impaired motor
Epilepsy: disease on one side of brain = convulsions on the other
Speculation: motor cortex = somatopically
Brodmann
Systematic investigation of variation of cortex cellular properties
Somatosensory map = organised adjacent to body surface
Motor map = musculature represented in adjacent parts
Empirical approach explaining
Dualism > materialism
Reductionism