🧠 Neurotransmission

📌 Definition Table

Term	Definition
Neurotransmitter	A chemical messenger that transmits signals across the synaptic gap from one neuron to another.
Synapse	The junction between two neurons where neurotransmission occurs.
Action Potential	An electrical impulse that travels down the neuron, triggering neurotransmitter release.
Excitatory Neurotransmitter	Increases the likelihood that the receiving neuron will fire an action potential (e.g., glutamate).
Inhibitory Neurotransmitter	Decreases the likelihood that the receiving neuron will fire (e.g., GABA).
Reuptake	The reabsorption of neurotransmitters by the presynaptic neuron after signal transmission.
Agonist	A chemical or drug that enhances the effect of a neurotransmitter.
Antagonist	A chemical or drug that blocks or reduces the effect of a neurotransmitter.
Serotonin	A neurotransmitter involved in mood regulation, sleep, and arousal.
Dopamine	A neurotransmitter linked with reward, motivation, and movement.
Acetylcholine (ACh)	A neurotransmitter involved in muscle contraction, learning, and memory.

📌Core Concepts
Neurotransmission is the process of communication between neurons through chemical messengers known as neurotransmitters.
When an electrical impulse reaches the end of an axon (the presynaptic terminal), it triggers the release of neurotransmitters into the synaptic cleft, where they bind to receptors on the postsynaptic neuron.

This process allows for rapid, targeted communication, influencing perception, emotion, cognition, and behavior.
Different neurotransmitters have distinct roles: dopamine in reward and motivation, serotonin in emotion and sleep, acetylcholine in memory, and GABA in anxiety regulation.

Understanding neurotransmission provides a biological explanation for behavior and insight into treatments for psychological disorders.

Mechanisms of Neurotransmission

Action Potential Generation:

• An electrical signal travels down the axon due to depolarization.

Vesicle Release:

• Neurotransmitters stored in vesicles are released into the synaptic cleft.

Receptor Binding:

• Neurotransmitters bind to receptor sites on the postsynaptic membrane.

Signal Transmission:

• Excitatory neurotransmitters (e.g., glutamate) increase neuron firing; inhibitory neurotransmitters (e.g., GABA) reduce it.

Reuptake/Degradation:

• Enzymes break down neurotransmitters or they are reabsorbed for reuse (e.g., serotonin reuptake).

📌Key Studies

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Rogers and Kesner (2003)

• Aim: To determine the role of acetylcholine (ACh) in memory formation.
• Method: Rats were trained to run a maze to find food. They were then injected with either scopolamine (ACh blocker) or saline (control).
• Findings: The scopolamine group took longer and made more mistakes in maze learning.
• Conclusion: ACh plays a key role in the formation of spatial memories.

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2. Antonova et al. (2011)

• Aim: To investigate the effect of blocking acetylcholine receptors on spatial memory in humans.
• Method: Double-blind, repeated measures fMRI study with 20 healthy males. Each participant received either scopolamine (ACh antagonist) or a placebo before performing a spatial memory task in an fMRI scanner.
• Findings: Participants under scopolamine showed reduced hippocampal activation.
• Conclusion: Acetylcholine is essential for encoding spatial memories; fMRI provides neural evidence for this mechanism.

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3. Fisher, Aron & Brown (2005)

• Aim: To examine dopamine’s role in romantic love.
• Method: fMRI scans of individuals “intensely in love” shown photos of their partners versus neutral acquaintances.
• Findings: Activation in dopamine-rich areas (ventral tegmental area, caudate nucleus) associated with reward and motivation.
• Conclusion: Romantic love involves dopamine pathways similar to addiction and reward circuits.

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4. Crockett et al. (2010)

• Aim: To investigate the role of serotonin in prosocial behavior.
• Method: Participants were given citalopram (a selective serotonin reuptake inhibitor, SSRI) or a placebo. They completed moral dilemmas involving harm to others.
• Findings: Participants on citalopram were less likely to inflict harm, showing increased prosocial responses.
• Conclusion: Increased serotonin levels promote prosocial and cooperative behavior by modulating emotional processing.

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5. Martinez & Kesner (1991)

• Aim: To study the role of acetylcholine in memory retrieval.
• Method: Rats injected with scopolamine (blocks ACh), physostigmine (enhances ACh), or saline before running a maze.
• Findings: Scopolamine impaired memory; physostigmine improved it.
• Conclusion: ACh directly facilitates memory encoding and retrieval—critical for learning processes.

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🧩 Evaluation

Strengths

• Triangulation of evidence: Both animal and human studies show consistent findings.
• Use of fMRI and controlled lab conditions enhances reliability.
• Demonstrates biological basis of learning, emotion, and memory.

Limitations

• Reductionist: Focuses narrowly on neurotransmitters, ignoring psychological and social influences.
• Ethical issues in animal research (injections, induced stress).
• Drug studies may have side effects that confound results.

Ethical Considerations

• Human studies (Antonova, Crockett) used double-blind designs and informed consent.
• Animal studies (Rogers & Kesner) minimized suffering but must justify the use of invasive techniques.

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