Biology of Mind: Key Concepts for Exam

Explore the brain–mind relationship: biology underpins psychological processes.
Historical ideas:
- Hippocrates located the mind in the brain.
- Aristotle believed the heart housed the mind.
Phrenology ( early 1800s):
- Studied skull bumps to infer mental abilities; debunked as a science, but it helped prompt localization-of-function ideas.
Modern view: different brain regions contribute to different aspects of behavior; functions are localized but integrated in networks.
Biopsychosocial system:
- Brain, body, and environment form nested systems (neuron → brain networks → body organs → person → family → culture).
- This integrated view is the biopsychosocial model (Engel, 1981).

Neuroplasticity = lifelong brain changes in response to experience; greatest early, but continues across the lifespan.
Examples illustrating learning-induced changes:
- London taxi drivers: extensive city navigation → enlarged hippocampus (memory for spatial layouts).
- London bus drivers (less complex routes): no similar neural reward.
- Well-practiced skills (e.g., piano playing) → expanded brain areas related to those skills.
- Sensory experiences (e.g., echolocation in the blind) recruit brain areas used by other senses.
Societal interventions and plasticity: early-life experiences (e.g., financial support) alter brain activity related to language and social cognition.
Cultural neuroscience: different cultures shape brain activation patterns in emotion and social processing.
Marion Diamond's work highlighted experience-driven brain changes and contributed to understanding brain plasticity.
Takeaway: the brain is a work in progress, sculpted by genes and experience; plasticity enables adaptation to new environments and learning demands.

Neurons are the basic information-processing units; other cells (glia) support them.
Neuron structure:
- Dendrites: receive signals.
- Cell body (soma): integrates signals.
- Axon: transmits signals to other neurons, muscles, or glands.
- Myelin sheath: fatty insulation increases signal speed.
- Glial cells: provide nutrients, insulation, guidance for connections, and help in learning and memory; higher glia-to-neuron ratio sometimes linked to complexity (e.g., Einstein brain).
Neuron communication basics:
- Signals are transmitted as electrochemical impulses across synapses (tiny gaps between neurons).
- Action potentials travel along the axon to communicate with target cells.

Resting potential:
- The outside of the axon has more positively charged ions (e.g., Na+); the inside is comparatively negative.
- The axon membrane is selectively permeable, maintaining this resting state.
Action potential (neural impulse):
- Triggered when excitatory signals outweigh inhibitory signals by a threshold (the neuron's "threshold").
- Sequential opening of ion channels along the axon (domino-like) causes depolarization, allowing Na+ to flood in.
- Propagates down the axon as a traveling electrical impulse.
Speed and scale:
- Conduction speeds range roughly from $2\ \text{mph}$ up to $200\ \text{mph}$ (≈ $320\ \text{km/h}$ ).
- Brain activity is measured in milliseconds (ms), while computer activity is in nanoseconds (ns): $1\ \text{ms} = 10^{-3}\ \text{s},\; 1\ \text{ns} = 10^{-9}\ \text{s}$ .
Signal intensity and coding:
- Most signals are excitatory or inhibitory.
- A stronger stimulus does not increase the strength of a single action potential; it increases the number of neurons firing and/or the firing rate of those neurons.
- The action potential is an all-or-none event: either the neuron fires or it does not.
Refractory period:
- After an action potential, a brief pause prevents immediate re-firing.

Neurons operate within networks; messages flow through a web of interconnected cells.
The nervous system is highly conserved across species, allowing study of simpler organisms to illuminate human brain function.
The integrated brain supports thoughts, memories, emotions, and behavior through dynamic, distributed processing.