IB Psychology Paper 1: Discuss the effects of one or more neurotransmitters on human behaviour.

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  This essay will discuss the effects of two neurotransmitters, serotonin and acetylcholine, on human behaviour. Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron to another. This process of neurotransmission is fundamental to brain function and, consequently, to behaviour. The central argument of this essay is that while neurotransmitters have a demonstrable effect on specific behaviours, this relationship is complex and explaining behaviour solely through neurochemistry is a reductionist approach. The discussion will be supported by research into serotonin's effect on prosocial behaviour and acetylcholine's effect on memory.

  One neurotransmitter with a significant effect on social behaviour is serotonin. While commonly associated with mood, serotonin is also implicated in regulating social decision-making. Lower levels of serotonin have been linked to antisocial and impulsive behaviour. To investigate this relationship experimentally, Crockett et al. (2010) studied the effect of serotonin on prosocial behaviour.

  Crockett et al. (2010) aimed to determine if serotonin levels would affect moral judgments in a prosocial context. The study used a repeated measures, double-blind design with 30 healthy volunteers. In one condition, participants were given a dose of citalopram, a selective serotonin reuptake inhibitor (SSRI) which acts as an agonist by increasing the concentration of serotonin in the synapse. In the other condition, they received a placebo. Participants were then presented with a series of moral dilemmas (the 'trolley problem'), which included impersonal scenarios (pulling a lever to divert a trolley) and personal scenarios (pushing a man off a bridge to stop a trolley). The findings were that in the personal scenario, participants in the citalopram condition were significantly less likely to push the man. The drug had no effect on the impersonal scenario. Crockett et al. concluded that serotonin reduces the acceptability of personal harm, thus promoting prosocial behaviour. This study demonstrates a clear effect of a neurotransmitter on behaviour: increased serotonin levels appear to modulate social judgment, making individuals more averse to harming others.

  However, the study has limitations. While the double-blind, repeated measures design is a strength, citalopram's effects are not 'clean'; it may have other effects that could be a confounding variable. Furthermore, the task involved hypothetical moral judgments, not actual behaviour, which limits its ecological validity. It is a logical leap to assume that a response to a dilemma directly equates to real-world prosocial action. This highlights the difficulty in operationalizing and measuring complex human behaviours.

  Another key neurotransmitter is acetylcholine (ACh), which is believed to play a crucial role in memory formation and consolidation, particularly within the hippocampus. To investigate this, researchers often use an antagonist, scopolamine, which blocks ACh receptor sites, to induce a temporary disruption of its function.

  Antonova et al. (2011) investigated the role of acetylcholine in the encoding of spatial memory. The study used a double-blind, placebo-controlled experiment with a sample of 20 healthy male adults. Participants were randomly allocated to one of two conditions: injected with either scopolamine or a placebo. They were then placed in an fMRI scanner while playing a complex virtual reality game (the 'Arena Task') where they had to navigate an arena to find a pole. After finding it, the screen would go blank for 30 seconds, and they were asked to actively rehearse the path to the pole. When the arena reappeared, they had to use their spatial memory to find the pole again. The study found that the scopolamine group took longer to find the pole and demonstrated a significant reduction in the activation of the hippocampus compared to the placebo group. The researchers concluded that acetylcholine plays a key role in the encoding of spatial memory in humans. This study provides strong evidence for the effect of ACh on the cognitive behaviour of memory, linking a specific neurotransmitter to a specific brain region and a measurable cognitive task.

  This study also has methodological considerations. The sample size was small and consisted only of males, which limits the generalizability of the findings. Furthermore, being injected and placed in an fMRI is a stressful experience, and the stress hormone cortisol could be a confounding variable affecting hippocampal function and memory. While the fMRI data provides objective evidence, the link between ACh and memory is still correlational; we cannot be absolutely certain of a direct cause-and-effect relationship, only that blocking ACh receptors impairs performance on this task.

  In discussing the effects of neurotransmitters, it is crucial to acknowledge the limitations of a purely biological explanation. Explaining complex behaviours like prosociality or memory solely through the action of a single neurotransmitter is highly reductionist. Behaviour is the product of an intricate interaction between biological systems, cognitive processes, and sociocultural factors. For example, prosocial behaviour is also heavily influenced by cultural norms and personal cognitions (empathy). Furthermore, the direction of causality is not always clear. For instance, does low serotonin cause antisocial behaviour, or does a lifestyle with limited positive social interaction lead to lower serotonin levels? This bidirectional ambiguity challenges simplistic causal claims.

  In conclusion, research has provided compelling evidence that neurotransmitters have a significant effect on human behaviour. Studies by Crockett et al. and Antonova et al. demonstrate that serotonin can modulate prosocial judgment and acetylcholine is vital for spatial memory formation. However, this 'discussion' must be tempered with critical awareness. The effects are not deterministic, and the methods used to study them have limitations. A holistic understanding requires acknowledging that neurochemistry is just one part of a larger, dynamic system that produces the vast spectrum of human behaviour.

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  How it meets the IB criteria

  • A — Focus on the question — The response is fully focused on the 'discuss' command term. The introduction explicitly defines the problem and sets out the essay's argument and structure. Each body paragraph directly links the research (Crockett, Antonova) back to the question by explaining how the neurotransmitter affects a specific 'human behaviour' (prosocial judgment, spatial memory). The dedicated discussion paragraph directly addresses the complexities and nuances implied by the command term.
  • B — Knowledge and understanding — The essay demonstrates detailed and accurate knowledge. It correctly defines neurotransmission and key terms like 'agonist' (in the context of citalopram being an SSRI) and 'antagonist' (scopolamine). The specific roles of serotonin and acetylcholine are accurately described, providing a solid theoretical foundation for the supporting research.
  • C — Use of research to support answer — Two relevant studies (Crockett et al., 2010; Antonova et al., 2011) are used effectively. Each study is thoroughly explained with clear details on the aim, method, findings, and conclusion. Crucially, the research is not just 'listed' but is integrated into the argument to actively support the claims being made about each neurotransmitter's effect on behaviour.
  • D — Critical thinking — Critical thinking is well-developed and consistent. Each study is evaluated for its methodological strengths and limitations (e.g., 'low ecological validity' for Crockett, 'small sample size' and 'confounding variables' for Antonova). The dedicated discussion paragraph elevates the response by addressing broader conceptual issues like reductionism and bidirectional ambiguity, synthesizing the points rather than evaluating them in isolation. This directly fulfills the 'discuss' requirement.
  • E — Clarity and organization — The essay is clearly organized and easy to follow. It has a clear introduction, distinct body paragraphs for each neurotransmitter/study, a separate paragraph for overall discussion, and a concise conclusion. Topic sentences are used effectively to guide the reader (e.g., 'One neurotransmitter with a significant effect... is serotonin.'), ensuring a logical and coherent flow throughout the response.

  Common ways to drop marks

  • Describing studies without evaluation: Students narrate the aim, method, and findings of a study but fail to discuss its limitations or implications, thus not meeting the 'discuss' command term.
  • Making deterministic claims: Writing 'serotonin causes prosocial behaviour' instead of using more nuanced language like 'serotonin appears to modulate...' or 'is correlated with...'.
  • Weak links to the question: The student describes the process of neurotransmission and a study in detail but fails to explicitly connect the findings of the study back to a specific 'human behaviour'.
  • Listing research instead of using it: Presenting two or three studies back-to-back without integrating them into a coherent argument or using them to compare, contrast, or build a discussion.

  Examiner tip: For 'discuss' questions, always dedicate a separate paragraph after presenting your evidence to critically evaluate the overall topic, addressing broader issues like reductionism, methodological limitations, and alternative explanations.

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