Case Studies: Serotonin: Crockett et al. (2009), Dopamine: Fisher et al. (2005), Freed et al. (2001)

Neurotransmitters are chemicals produced and released by neurons in the nervous system and they can have an inhibitory/ excitatory effect.

Neurotransmitters & their functions:

• serotonin = satisfaction
• dopamine = reward,
• endorphins increase pleasure,
• oxytocin = “bonding” hormone (a hormone that acts as a neurotransmitter)

This video tickles me lol. 1:12 for Dopamine; 2:50 for Serotonin; 4:20 for Ocytocin

Serotonin, known for stabilizing mood, has garnered attention in understanding aggressive/ prosocial behavior.

Crockett et al.’s (2009)

Crockett et al.’s (2009) study revealed that participants with lower serotonin levels exhibited higher retaliatory aggression during game-playing scenarios. In a sample of 24 participants, those who took citalopram, a serotonin reuptake inhibitor drug (SSRI), were less inclined to consider actions that may cause harm and displayed less aggression.

Participants were asked hypothetical questions
Would you push someone in front of a train if it meant saving five other people? 
Would you flick a switch so that a train hits one person instead of five?

In the scenario requiring the participants to think about harming someone, ie. pushing a man off the bridge which will help avoid killing 5 other people, participants who took citalopram were less likely to push the man off.

Individuals with heightened serotonin levels demonstrated greater compassion in emotional moral dilemmas compared to those with lower levels. Those with lower serotonin levels showed they were less likely to prioritize utilitarian outcomes.

Conclusion: suggests that serotonin modulates perceptions of harm, making it appear less acceptable. Higher serotonin levels also encouraged prosocial behaviors.

Strengths	Weaknesses
– Adoption of double-blind procedure enhances internal validity – Screening participants for psychiatric and neurological disorders before the study improves result reliability	– Findings may have limited generalizability, as the study was conducted in a controlled laboratory setting with specific experimental conditions – Small sample population makes it difficult to apply findings to wider population

Dopamine

Fisher et al. (2005)

Fisher, Aron, and Brown’s (2005) study explored neural mechanisms underlying romantic love, particularly the levels of dopamine in brain responses to loved ones.

Dopamine, an excitatory neurotransmitter, plays multifaceted roles in motivation, pleasure, and emotional regulation. Recruiting 10 men and 7 women who reported being “intensely in love,” the study employed functional magnetic resonance imaging (fMRI) to observe brain activity while participants viewed photographs of their beloved and emotionally neutral acquaintances.

During the fMRI scans, participants engaged in a standardized procedure involving alternating stages of viewing photographs and performing filler activities. Notably, the fMRI results revealed distinct patterns of brain activation in response to images of loved ones, primarily in dopamine-rich neural systems such as the ventral tegmental area (VTA). Prior research has shown the VTA is an area of the brain associated with “pleasure, general arousal, focused attention and motivation to pursue and acquire rewards.” (Fisher, 2005).

Repeated observations of dopamine-related activity in response to romantic stimuli underscore the role of dopamine in romantic love. This study sheds light on the intricate interplay between neurotransmitters and human emotions.

Dopamine’s role in Parkinson’s disease sheds light on its importance in motor functions.

Freed et al. (2001)

Freed et al. (2001) conducted a study implanting dopamine-producing neurons into Parkinson’s patients, a degenerative disorder affecting motor functions.

They conducted a study with 40 patients aged 34–75, divided into experimental (nerve cell transplant) and control (sham surgery) groups. The transplant involved dopamine-producing neuron tissue from embryos, targeting the putamen. While the experimental group received the transplant, the control group underwent a similar procedure without brain penetration.

While younger patients experienced symptom reduction, older patients saw less benefit, possibly due to reduced neuroplasticity. Activation in dopamine-rich areas like the ventral tegmental area (VTA) occurred when participants viewed pictures of loved ones, emphasizing dopamine’s role in reward processing and emotional bonding.

Strengths	Weaknesses
– Longitudinal Design: Examines patients over substantial period (14 years on average), allowing for the assessment of long-term effects	– Sample Size: Limited sample size (40 patients) may restrict the generalizability of findings/ statistical power – Those assigned to control group may be deprived of potentially life-saving (dopamine) treatment

Past Exam Questions
Explain how one or more neurotransmitters affect human behaviour. [8 marks]

Read here for more on the Nervous System
Read here for more on Oxytocin