Neuroscience: Action Potentials and Synapses

Depolarization, Repolarization, and Hyperpolarization

• Depolarization: The membrane potential becomes less negative, moving closer to zero.
• Repolarization: The membrane potential returns to its negative resting state after an action potential.
• Hyperpolarization: The membrane potential becomes even more negative than the resting potential, making it less likely for an action potential to occur.

Refractory Periods

• Absolute Refractory Period: The neuron cannot fire again, regardless of the strength of the stimulus.
• Relative Refractory Period: The neuron can fire, but only with a stronger than usual stimulus.

All-or-None Law

• Neurons follow an all-or-none principle: They either fire an action potential or they don't.
• Stronger stimuli increase the frequency (how often) an action potential is fired, not the strength of the action potential.

Synaptic Transmission

• A synapse is the junction between the axon terminal of one neuron and the dendrite or cell body of another neuron.
• Excitatory Synapses: Increase the likelihood of the postsynaptic neuron firing an action potential.
  • Neurotransmitters like glutamate cause the postsynaptic neuron to become more positive.
  • This is called an Excitatory Postsynaptic Potential (EPSP).
• Inhibitory Synapses: Decrease the likelihood of the postsynaptic neuron firing an action potential.
  • Neurotransmitters like GABA make the postsynaptic neuron more negative.
  • This is called an Inhibitory Postsynaptic Potential (IPSP).

Plasticity

• Synapses can change their strength and effectiveness due to learning or experience.

Some Neurotransmitters

• Dopamine: Plays a role in movement, learning, attention, and emotion.
• Serotonin: Influences mood, hunger, sleep, and arousal. Low levels are linked to depression.

Dopamine Hypothesis of Schizophrenia

• Excessive dopamine activity is thought to contribute to schizophrenia.

Agonists and Antagonists

• Agonists: Drugs that mimic the effects of neurotransmitters.
  • Amphetamines are examples of agonists.
• Antagonists: Drugs that block the effects of neurotransmitters.
  • Chlorpromazine is an example of an antagonist.

Learning and Synapse Plasticity

• Habituation: A decrease in response to a repeated stimulus.
• Sensitization: An increase in response to a repeated stimulus.

Brain Plasticity:

• Neural Reorganization: The brain can adapt and reorganize its neural pathways in response to experience or damage.
  • Example: The occipital lobe (vision) may take on new roles in blind individuals.
• New Neuron Generation: The adult brain can continue to generate new neurons.

Brain Structure Change with Experience

• Changes in brain structure can occur with experience.
  • Example: Taxi drivers have larger hippocampi (spatial memory).
• Damage to the brain can lead to neural reorganization.

Notable Examples of Brain Plasticity

• Taxi drivers: Enlargement of the hippocampus.
• Musicians: Changes in the motor cortex due to years of practice.
• Bilinguals: Enlarged parietal cortex due to language processing.

Split-Brain Experiments

• The corpus callosum is a bundle of nerve fibers that connects the left and right hemispheres of the brain.
• Split-brain procedure: The corpus callosum is severed to treat epilepsy, preventing seizures from spreading between hemispheres.
• Split-brain patients: Show how the brain hemispheres process information independently.
  • The left hemisphere controls language and speech.
  • The right hemisphere is involved in spatial and non-verbal tasks.

Damage to the Right Parietal Lobe

• Leads to hemineglect or hemi-inattention, where individuals ignore the left side of their visual field.

Key Findings from Split-brain Studies

• Each hemisphere processes visual information from the opposite visual field.
• Split-brain patients can draw or point to objects presented to the right hemisphere (left visual field), but can't name them.
• The left hemisphere is responsible for verbal processing, while the right hemisphere excels in nonverbal tasks.

Consciousness

• Consciousness: One's subjective experience of the world.
• Sensory awareness: Awareness of the environment.
• Direct inner awareness: Awareness of one's own thoughts and feelings.
• Personal Unity: The feeling of being a unified self.
• Waking state: The state of being awake and aware.

Attention: Gateway to Consciousness

• Attention is crucial for consciousness.
• Change Blindness: Failure to notice large changes in the environment when attention is elsewhere.
• Inattentional Blindness: Failure to notice an obvious object in the visual field when attention is focused on something else.

Types of Attention

• Exogenous Attention: Automatic, stimulus-driven attention.
• Endogenous Attention: Voluntary, goal-driven attention.

Dichotic Listening and Change Deafness

• Dichotic Listening Task: Participants focus on one auditory message while ignoring another.
• Change Deafness: Even with focused attention, we may not notice semantic changes in an auditory stream.

The Stroop Effect

• The brain's automatic processing of word meanings interferes with identifying the color of the ink.

Divided Attention and Dual Processing

• Dual Processing: Performing two tasks simultaneously.
• Divided Attention: Trying to focus on multiple tasks at once.
• True multitasking is difficult for the brain, especially when both tasks require effort.

Hemineglect

• Individuals ignore one side of their visual field, often due to damage in the right parietal lobe.

Brain Waves and Consciousness States

• Gamma Waves: Problem solving, concentration.
• Beta Waves: Alert, awake state, active thinking.
• Alpha Waves: Relaxed, calm state.
• Theta Waves: Light sleep, deep meditation, visualization.
• Delta Waves: Deep sleep, physical restoration.

Sleep Stages and Brain Activity

• Stage 1: Light sleep, characterized by theta waves.
• Stage 2: Deeper sleep, characterized by sleep spindles and K-complexes.
• Stage 3 & 4: Deep sleep, dominated by delta waves.
• REM Sleep: Rapid Eye Movement sleep, brain activity similar to wakefulness, dreams occur in this stage.

REM vs. NREM Sleep Across Ages

• Infants: Spend more time in REM and NREM sleep.
• Adults: Sleep 7-8 hours, with about 20-25% in REM sleep.
• Elderly: Sleep less, with reduced REM sleep and lighter sleep.

Altered States of Consciousness

• Meditation: Shifting focus inward, leading to altered perception and relaxation.
• Hypnosis: A highly focused, suggestible state where perception and behavior can be altered.
• Psychoactive drugs: Substances that alter perception, mood, and thought patterns.
• Sleep: A naturally occurring state with distinct stages.

Key Sleep Terminology

• K-Complex: A large wave in stage 2 sleep that helps protect the sleeper from waking.