Neuroscience: Historical Perspectives
Early theories: the mind and body
Localisation and neuroanatomy
The Neuron Doctrine
Localisation: Phrenology to cortical topography
Plato: the brain conveys sensations and once these settle in the mind, knowledge, memory and opinions are produced.
Egypt! 48 cases of head injuries investigated: noted the importance of the brain and it's role in behaviour but believed the heart was the 'seat of the soul' (mummification)
Homer: One overall 'soul' called 'psyche': non-localised soul which represents individual life/identity. soul is active/non-silent only in dreams and abandons the body at death
three additional types of 'body soul' located in chest
Noos: reasoning
Menos: aggression
Thymos: emotion
Natural Philosophers: systematically reject supernatural and try to understand everything through material mechanisms
e.g. Anaximenes who theorised that the origin of human thoughts is air.
Encephalocentrism vs Cardiocentrism debate
Where lies the 'seat of human consciousness, sensation and knowledge'? Brain vs heart!
Anatomical dissection: Alcmaeon of Croton: Encaphalocentrism: sensory and cognitive significance of brain lead him to believe it was where consciousness resides & if the brain is disrupted then so are all senses. Also, believed that man has understanding whilst animals only have sensations
Western Medicine: Hippocrates: noted 2 hemispheres of the brain; 'lateralization' and rejected possibility of a 'sacred' cause of epilepsy: said it was a disease of the brain. Believed the brain is the most powerful organ
Encephalocentrism but also cardiocentrism!: 3 species of soul
Thymos: perishable soul, responsible for emotions, located in chest/heart
Epithemetikon: perishable soul, responsible for urges e.g. hunger, passion, located in liver
Logos: immortal, divine, localised in head
Aristotle: 3 soul faculties, all reside in heart: cardiocentrism
Sensitive/motor: animals
Nous: humans, an immaterial soul
Vegetative: plants and some animals
Believed the role of the brain to be: diminish heat of blood generated by heart and generate sleep
Cardiocentrism: THE HEART IS...: affected by emtion, all animals have one, source of blood, warm, connected to whole body, essential, formed first in foetus, sensitive to pain, central in body!
Galen of Pergamon: Encephalocentrism: anatomical methodology, brain receives sensations and generates understanding.
"apodeictic proofs" provided: brain and spinal cord source nerves. Spinal cord originates from brain
Experiments: severing throat nerves in pig inhibited squealing (but still breathing), concluded that voice comes from brain and not the heart.
Soul: communicates with the body via spirits, through 3 ventricles (brain cavities!) & travel through body via nerves.
Debate continued into the Renaissance!
13th Century: the mind and brain are related but seperate
Magnus brain is the centre of mental activity: sensation, rationing, memory. Mind and brain inextricably linked, but mind immaterial and resides in ventricles.
15th century: the Rebirth of Neuroanatomy!
Da Vinci: anatomical contribution of structure of the ventricles. Believed soul resides in ventricles rather than tissue because it is incorporeal.
16th century: Non-Ventricularist
rejected previous theory! Evidence that all mammals have the same anatomical organisation as humans but do not have the same intellect. Believed that rather than the soul, it was animal spirits which reside in ventricle and follow nerves to organs.
17th Century: Cartesian Legacy
Descartes: brain and behaviour mediated by a mechanical theory that nerves are hollow with fluid flowing through them - 'Balloonist' Theory. Believed mind located in pineal gland. Dualism mind and body are separate!
⛔Ghost in the machine: Cartesian Gap how could something immaterial influence something material?
Pineal gland: small endocrine gland in brain between two hemispheres (central so logical to place mind here), it produces melatonin.
Willis: post-mortem examinations, concluded that psychological attributes are heavily reliant on the cortex! Dualism but believed the point of contact between mind and body is the cortex. ⛔Cartesian Gap
18th century was useless!
19th century: Advances in microscopy, improved histology, debate about nervous system organisation, Fritsch & Hitzig
advancing technology aided advancement in understanding of the nervous system and individual nerve cells.
Dendrites, cell body, axons identified.
Reticularists v Cell Theorists
R: believe NS is a large network of tissue (reticulum), formed by fused nerve cells. "The whole brain is a syncytium" meaning a large, cell-like structure. Von Gerlach
C: believe that NS consists of distinct nerve cells. Controversial theory that autonomous life should be attributed to cells. Virchow "omnis cellula e cellula" cells can only multiply from cells.
Both: use the same methods but came to different conclusions ⚠low magnification and poor resolution of microscopes available at the time
1820 Purkinje cells: Johannes Evangelista Purkinje: discovery of these cells made him famous, they are among the largest cells in the vertebrate brain
Golgi staining the silver nitrate method invented by Golgi in 1873
Golgi believed his observations of cerebellar tissue etc were evidence of a diffuse nerve network hence supporting reticulum approach - as he observed continuous network rather than discrete nerves.
"Rete Nervose Diffusa" in Italian which literally translates to widespread nerve network
a more holistic approach
Ramon y Cajal neuroanatomist: The Neuron Doctrine!: acceptance of the neuron as anatomical and functional unit of the nervous system
"the relationship between nerve cells was not one of continuity but rather of contiguity" --> not continuous, just in close proximity
1887: new staining method! fixative and silver nitrate twice to get deeper staining... lead to observation in chicken cerebellum samples that dendrites reside at axon endings.
"each cell is a totally autonomous physiological canton" Cell theory
Waldeyer: coined the term 'neuron' in 1891
Investigated nervous conduction: direction of impulses and idea of synapses.
Won Nobel Prize (against Golgi!)
won Nobel Prize (against Cajal!)
1950s: Electron microscopy techniques: Bennett: Reaffirmed Cajal's proposal that there is a gap (synapse) between all nerve endings, even when greatly intimate.
Main Tenets of the theory
Neurons are discrete not continuous
Neurons have 3 parts: dendrite, cell body, axon
The fundamental structure/ unit of the NS is the neuron
information flows in one direction along the neuron
Reasons for delay: why did it take so long to realise this?
nerve cells/ NS have very complex structure!
belief of cell continuity was necessary for cell interaction at that point of theoretical knowledge: i.e. did not make sense to scientists that discrete units could interact- they must be connected!
Technical advancement of histological prep and microscope accuracy
1585: von Grafenberg: early observations of brain damage - although the tongue was not paralysed the patient could not speak: Same as Galen - voice must come from the brain
19th century
Brain Equipotentiality theory: all parts of the brain have equal significance in functions
Localization theory: high degree of specialization of brain areas' functionality Gall & Spurzheim
Phrenology: Principles: Many organs in the brain, responsible for particular skills. Bigger = more powerful. The brain shape is determined by organ development. Skull surface provides accurate index of brain. Can analyse personality using this method. Phrenometer: machine which measures 'bumps' on skull.
in reality, skull shape has nothing to do with cognition.
but they (Gall & Spurzheim) did make important observations, such as the fact that the brain is folded.
Against localization: Flourens: brain lesions in animals did not cause specific behavioural deficits, hence concluded that brain shares functionality: Aggregate field theory
Brain mapping: lesions: Broca's area & aphasia: left inferior frontal cortex damage thought to be cause of language/speech inhibition.
Wernicke's aphasia: damage to posterior left hemisphere: language understanding rather than speech.
"the first brain map": Fritsch & Hitzig: dogs' cortex electrically stimulated resulted in muscular contractions. ✅ localization, as findings generalised to say that all functions are linked to specific areas.
Jackson: Epilepsy: often convulsions are on one side of body only - perhaps because the organic disease is only affecting one hemisphere?... motor cortex organised somatotopically: i.e. hands are most sensitive/wide range of movement so must receive largest representation in cortex.
more research builds bigger picture: Penfield
Homonculus!
Anatomy & brain mapping: Brodmann: systematic investigation of primates developed somatosensory map: adjacent areas of body represented in adjacent areas of cortex.
Mapping and understanding of 'mind': explain beh in mechanistic terms, dualism -> materialism, reductionism: explain brain in terms of its parts ❌ does this really inform cognitive models? are mind and brain separate?