Consciousness: How Our Brains Turn Matter Into Meaning

1. What is Consciousness?

• Aristotle believed that consciousness exists as a continuum of different types of souls:
  • Plants have a vegetative or nutritive soul, which controls their growth, nutrition and reproduction.
  • Animals have, in addition, a sensitive soul, which allows them to perceive things and move about, and they also have fears and desires.
  • Humans have, in addition, a rational soul that allows them to reason and reflect.
• Locke and Hume came up with a properly materialist view of consciousness, but their explanations did not explain how each individual mind feels like a unified, individual phenomenon, rather than just a mass of unconnected experiences (binding problem)
• Chalmers sees the hard problem of consciousness as explaining this subjective sense we have as individuals of being us, with all that implies in terms of our specific responses to, say, a sunset or a work of art, the particular way we felt when we first fell in love or any personal experience, in purely material terms.

2. Tools and Symbols

• Parrington argues that human self-conscious awareness arose as a consequence of two other unique human attributes - our capacity for language and our ability to continually transform the world around us by designing and using tools.
• Engels, in 1876, proposed that humans first began to diverge significantly from other primates when our ancestors started walking on two legs. This freed the hands for using and designing tools in a systematic way to transform the world around them. Importantly, such design and subsequent use of different types of tools was carried out with other proto-humans in a socially cooperative manner. Because of the need to communicate with their neighbors about how to carry out such innovative actions, our ancestors also began to develop the first forms of language. Subsequently the development of both systematic tool design and use, and language, led to a dramatic growth and restructuring of the brain.
• Practically all of our interactions with the world are through tools that we have created.
• Human language, is an interconnected system of abstract symbols, linked together by grammar in such a way that it can convey complex meaning. It is for this reason that only human beings are able to use language to convey complex ideas like past, present, and future, individual versus society, location in space, and even more abstract concepts.
• We can see tool use and language as activities that do not just guide our interactions with the external world, but also act as "mental tools" that have transformed the brain in the process.
• Vygotsky argued that egocentric speech - children's tendency to talk to themselves as they play - is the first stage in a child starting to organize their actions using words and that while this form of speech seems to disappear, what is actually happening is it becomes internalized as "inner speech", which in adults plays a central role in the organization and development of our thoughts.
• Inner speech differs from outer speech in some important ways. It is likely to be much more rapid, and far more fluid in meaning, than the speech we use in conversation with others. There are also probably different types of inner speech, ranging from that which emerges from our innermost, half-formed thoughts to the type that structures our outer speech when we express ourselves to others.

3. Nerves and Brains

• Neurons contain:
  • A cell body
  • Dendrites - Tendrils that receive incoming signals from other neurons
  • An axon - A long protuberance that conveys signals to the next neuron in the circuit
• When a neuron is stimulated through its dendrites, this triggers an electrical impulse called an "action potential", which races along the axon at speeds that can reach around 200mph in the fastest human neurons. The speed at which impulses can travel along an axon are greatly enhanced by a structure called a "myelin sheath". This is a fatty layer that both protects the axon but also allows the neural signal to jump between gaps in the sheath in a process called "saltatory conduction". At the end of the axon, the electrical impulse is transmitted to a dendrite on the next neuron in the circuit, at a gap between neurons called a "synapse". The action potential does this by stimulating the release of a chemical called a "neurotransmitter" into the synaptic gap. The neurotransmitter diffuses across the gap and, at the other side, it acts like a key in a lock to trigger a cellular response that activates a new action potential in the target neuron.
• The human brain is estimated to contain around 86bn neurons, linked by 100tn connections.
• Neurons make up half the brain. The rest is made up of glial cells including oligodendrocytes, astrocytes, and microglia.

4. Evolving Minds

• Jellyfish are a simple type of large multicellular organism whose nervous system consists of:
  • Sensory neurons - Which pick up signals from the environment.
  • Motor neurons - Which trigger a response in the organism
  • Interneurons - Which coordinate these two activities in the central nervous system (CNS).
• The human brain has three main parts:
  • The forebrain - Includes:
    • The Cerebellum - which has two hemispheres and a highly folded surface cortex
    • The Cortex - Is particularly developed in humans, twice the expected area for a primate of our size
      • Broca's area - For producing words
      • Wernicke's area - For understanding words
      • Sensory and motor maps, with most space taken up by nerves going from and to the lips, tongue and pharynx and to and from the hands and digits.
    • The Limbic System - emotional or lizard brain
      • Thalamus - Central postal-sorting depot channeling information into and out of the cortex
      • Hypothalamus - Underneath the thalamus, regulates thirst, hunger, desire, reproduction, and the body clock
      • Amygdala - Plays a central role in processing emotions, being involved in generating fearful, but also pleasurable sensations
      • Hippocampus - Plays important roles in memory
  • The midbrain - alos involved in processes such as vision, hearing, and movement
  • The hindrain - Includes
    • The Pons, which controls sleep
    • The medulla, which regulates vital functions such as breathing and heart rate
    • The cerebellum (little brain) - With, once again, two hemispheres and a highly folded surface. Involved in regulating and coordinating movement, posture, and balance and also in creativity and imagination.

5. Thought and Reason

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6. The Sensual World

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7. Learning and Memory

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8. Mind Chemistry

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9. Philosophy of Mind

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10. Individual and Society

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11. Information and Meaning

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12. Chance and Design

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13. Structure and Function

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14. Circuits and Waves

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15. Free Will and Selfhood

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16. Consciousness and the Unconscious

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17. Modernity and Its Contradictions

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18. Sanity and Madness

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19. How Ideas Change

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20. Future of Mind

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