🧠 How Brain Chemicals Affect Your Thoughts, Feelings, and Actions

Your brain and body are constantly being influenced by natural chemicals. These neurotransmitters and hormones are like messengers — they help you feel things, focus your thoughts, and decide how to act. Here's what the main ones do:

💭 Thoughts & Focus

• Dopamine: Your brain’s “goal getter.” It gives you the drive to chase rewards, learn new things, and build habits.
• Acetylcholine (not in the table but worth noting): Helps you stay focused and remember stuff.

💓 Feelings & Mood

• Serotonin: Helps you feel stable and calm. Low levels are linked to depression and anxiety.
• Cortisol: The stress chemical. It helps you handle tough situations, but too much over time can wear you down emotionally.
• Oxytocin: The “bonding” hormone. It kicks in when you feel close to someone or are caring for others.

🧘‍♀️ Calm & Safety

• GABA: Your brain’s “brake pedal.” It slows things down, helps you relax, and fights anxiety.
• Melatonin: Signals your body that it’s time to sleep. It rises at night to make you drowsy.

⚡ Action & Drive

• Norepinephrine: Gives you that alert, on-edge feeling when something important is happening — like during a test or emergency.
• Testosterone: Fuels confidence, assertiveness, and competition. Everyone has it (not just men), but levels vary.

🧩 What It All Means

Your feelings and actions aren’t random. They’re shaped by this mix of chemicals working together. For example:

• Feeling super focused and motivated? Likely high dopamine and norepinephrine.
• Calm and content? Your GABA and serotonin are doing their job.
• Stressed or anxious? Maybe your cortisol is too high or GABA too low.
• Struggling to sleep? Could be a melatonin issue.

✅ Bottom Line

Your brain chemistry plays a huge role in:

• How you feel
• What you pay attention to
• How you respond to life

Understanding these chemicals can help you build better habits, manage your emotions, and even improve your mental health.

🔹 Dopamine

• Function: Reward, motivation, reinforcement learning, movement
• Where: Mesolimbic pathway (reward), nigrostriatal pathway (motor control)
• Evidence:
  • Central to incentive salience (Berridge & Robinson, 1998)
  • Altered in Parkinson’s disease (low dopamine) and addiction (highly dysregulated reward prediction)
• Key Effect: Drives goal pursuit, habit formation, reinforcement

🔹 Serotonin (5-HT)

• Function: Mood regulation, social behavior, impulse control, sleep
• Where: Produced in the raphe nuclei, acts widely in the brain
• Evidence:
  • SSRIs improve depressive symptoms by enhancing synaptic serotonin (Cipriani et al., 2018, Lancet)
  • Involved in emotion regulation and aggression inhibition (Carver et al., 2008)
• Key Effect: Regulates emotional balance and impulse inhibition

🔹 Norepinephrine (Noradrenaline)

• Function: Alertness, attention, arousal, fight-or-flight
• Where: Locus coeruleus origin, widespread cortical influence
• Evidence:
  • Key in stress response and cognitive readiness (Arnsten, 2009)
  • Altered norepinephrine linked to PTSD, ADHD
• Key Effect: Increases arousal, vigilance, and stress reactivity

🔹 GABA (Gamma-Aminobutyric Acid)

• Function: Brain’s primary inhibitory neurotransmitter
• Where: Found throughout cortex, basal ganglia, cerebellum
• Evidence:
  • GABAergic drugs (e.g., benzodiazepines) reduce anxiety (Lydiard, 2003)
  • Deficits linked to epilepsy, panic disorder, insomnia
• Key Effect: Calms overactive neural circuits, reduces anxiety

🔹 Glutamate

• Function: Brain’s main excitatory neurotransmitter; essential for learning and memory
• Where: Widespread in CNS, especially hippocampus
• Evidence:
  • Synaptic plasticity via NMDA/AMPA receptors (Malenka & Bear, 2004)
  • Excess = neurotoxicity in stroke, ALS, Alzheimer’s
• Key Effect: Increases signal strength, critical for learning

🔹 Acetylcholine

• Function: Learning, attention, memory, REM sleep
• Where: Basal forebrain and brainstem projections to cortex and hippocampus
• Evidence:
  • Disruption linked to Alzheimer’s disease
  • Nicotine enhances cholinergic transmission, improving attention short term
• Key Effect: Supports focused attention and encoding new information

🧬 HORMONES (Long-Term Systemic Regulators)

Hormones act more slowly but influence broader patterns like stress response, mood, sleep, bonding, and risk-taking.

🔹 Cortisol

• Function: Primary stress hormone, mobilizes glucose for energy
• Where: Secreted by adrenal glands under control of HPA axis
• Evidence:
  • Chronic elevation linked to depression, insomnia, cognitive decline (McEwen, 1998)
  • Diurnal cortisol rhythm dysregulated in PTSD and MDD
• Key Effect: Triggers energy release, increases alertness under threat

🔹 Adrenaline (Epinephrine)

• Function: Acute fight-or-flight hormone
• Where: Secreted by adrenal medulla
• Evidence:
  • Rapidly increases heart rate and respiration during stress
  • Acts alongside norepinephrine in acute stress states (Sapolsky, 2004)
• Key Effect: Prepares body for immediate action

🔹 Oxytocin

• Function: Bonding, empathy, trust, social affiliation
• Where: Synthesized in hypothalamus, released by posterior pituitary
• Evidence:
  • Facilitates pair bonding and parental behavior in mammals (Feldman, 2012)
  • Intranasal oxytocin enhances emotion recognition in some studies
• Key Effect: Enhances social connection and emotional trust

🔹 Testosterone

• Function: Aggression, competitiveness, dominance, libido
• Where: Gonads (testes, ovaries), regulated by hypothalamic-pituitary-gonadal axis
• Evidence:
  • Related to dominance motivation, not just aggression (Carré & Olmstead, 2015)
  • Sensitive to contextual factors like status threat
• Key Effect: Influences social dominance and risk preferences

🔹 Estrogen & Progesterone

• Function: Emotional regulation, cognitive flexibility, bonding
• Where: Ovaries; modulate serotonergic, dopaminergic systems
• Evidence:
  • Estrogen modulates hippocampal plasticity (Woolley, 1998)
  • Fluctuations tied to perimenopausal mood changes, PMDD
• Key Effect: Influence mood stability, emotional sensitivity

🔹 Melatonin

• Function: Regulates circadian rhythms and sleep
• Where: Pineal gland, secreted in darkness
• Evidence:
  • Increases sleep onset and improves sleep quality
  • Disturbed in insomnia, SAD, shift work disorder
• Key Effect: Promotes sleep and synchronizes biological clock

Sources & Further Reading

• McEwen BS (1998). “Stress, adaptation, and disease.” Annals of the NY Academy of Sciences.
• Berridge KC & Robinson TE (1998). “What is the role of dopamine in reward?” Brain Research Reviews.
• Arnsten AFT (2009). “Stress signaling pathways that impair prefrontal cortex structure and function.” Nature Reviews Neuroscience.
• Sapolsky RM (2004). Why Zebras Don’t Get Ulcers.
• Feldman R (2012). “Oxytocin and social affiliation.” Hormones and Behavior.
• Cipriani A et al. (2018). “Comparative efficacy and acceptability of 21 antidepressant drugs.” The Lancet.
• Carver CS, Johnson SL, Joormann J (2008). “Serotonergic function, two-mode models of self-regulation.” Psychological Bulletin.