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13 May 2025
8 Min Read
Dr Henkie Lai (Academic Contributor)
Have you ever spent ages rewriting a text message, only to hit send and instantly regret it? Or maybe you’ve blurted out an answer in class before really thinking—then realised you got it completely wrong?
Overthinking and impulsivity might seem like total opposites. One has you tangled in endless mental debates, while the other pushes you to act without hesitation. But here’s the twist—they both stem from the same source: your brain’s decision-making network.
Think of your brain as a busy operations centre. Different ‘departments’ are in charge of logic, emotion, habits, and evaluation. When they work well together, you make thoughtful, timely decisions. When they don’t, things go sideways.
When these systems are out of sync, problems arise. An overactive prefrontal cortex may lead to constant mental processing—evaluating every possibility and making it difficult to act. On the other hand, when the amygdala or striatum dominates, you might act on instinct or habit before you've had a chance to reflect.
Maybe you’ve rehearsed what to say for a class presentation countless times, planning every word. But when you get up in front of the room, your mind goes blank and you start speaking off the cuff—too fast, too soon. That’s the emotional brain hijacking the logical one under pressure.
Your brain relies on neurotransmitters—chemical messengers that help different brain regions communicate and function. These chemicals play a key role in how you make decisions and manage emotions.
One of the most well-known neurotransmitters is dopamine, often associated with pleasure and reward. When your dopamine levels are high, you may feel a surge of motivation and excitement that encourages impulsive behaviour—like clicking ‘buy now’ on something expensive without fully thinking it through. In contrast, low dopamine levels can leave you feeling mentally sluggish and indecisive, even when faced with simple decisions like choosing what to eat.
Another important chemical is serotonin, which helps regulate mood and thought patterns. If serotonin levels drop too low, anxious thoughts and obsessive overthinking may take hold. However, too much serotonin can sometimes dull your willingness to take necessary risks, leading to hesitation or missed opportunities.
Then there’s cortisol, your body’s primary stress hormone. When you’re under pressure—whether from an exam, argument, or tight deadline—cortisol surges through the brain. This can suppress the rational functions of the PFC and hand control over to the amygdala. In those moments, your body reacts with instinct rather than reason.
Think back to a time when you panicked halfway through an exam and started rushing through the questions, maybe even skipping a few. That wasn’t just nerves—cortisol was hijacking your brain’s logic system and fast-tracking you into survival mode.
Psychologist Daniel Kahneman described our decision-making process using the concept of System 1 and System 2 thinking. System 1 is fast, emotional, and automatic—perfect for reacting quickly. System 2 is slow, rational, and deliberate—ideal for analysing complex problems. Your brain constantly switches between the two, depending on the situation.
Overthinking tends to happen when your brain is overwhelmed with information. The PFC tries to examine every detail and possibility, but with no clear answer, it stalls. This is especially true when there’s fear of making the wrong decision. The anterior cingulate cortex keeps flagging potential risks, causing hesitation to grow even stronger.
Impulsivity, by contrast, often kicks in when time is tight or stakes feel high. The amygdala bypasses careful analysis and pushes for immediate action. If there’s a reward in sight, dopamine floods the system and encourages you to act now—sometimes too fast.
You might recognise this pattern from your own experience. Maybe you confidently picked an answer on a multiple-choice test, then started second-guessing it. At the last second, you changed your answer—only to realise your first choice was correct. That switch from intuition to over-analysis is your brain flipping between systems under pressure.
The exciting thing about your brain is that it isn’t fixed. Thanks to a process called neuroplasticity, your brain can rewire itself based on how you use it. With the right strategies, you can train your brain to find a better balance between careful thinking and confident action.
One way to strengthen your decision-making ability is by actively engaging your prefrontal cortex. Activities such as solving puzzles, playing strategic games like chess, writing reflective journals, or even participating in classroom debates all challenge your brain to think critically and analytically.
Regulating your brain’s chemical environment also helps. Physical exercise boosts levels of dopamine and serotonin naturally, while regular mindfulness or breathing techniques reduce cortisol and calm emotional responses. Sleep, hydration, and nutrition also play major roles in maintaining mental clarity.
Simple decision strategies can also reshape your habits. One example is the 10-minute rule—taking a brief pause before making any major decision. This small delay gives your brain time to shift into System 2 thinking, so you're less likely to act impulsively.
In fact, studies have shown that people who practise mindfulness regularly tend to have increased grey matter in the PFC. That means more brainpower for reflection, control, and calm decision-making.
In today’s digital age, constant exposure to fast content and nonstop notifications can disrupt our dopamine system, making us more impulsive and harming focus. But with mindful habits and digital breaks, we can retrain our brains and restore balance.
Overthinking and impulsivity aren’t flaws—they’re natural features of how the brain responds to information, emotion, and uncertainty. One leans on caution and analysis, while the other relies on speed and instinct. The problem comes when one consistently overrides the other.
Fortunately, your brain is not set in stone. It learns from every choice you make. Through mental training, emotional regulation, and smart decision-making techniques, you can fine-tune how your brain responds in the moment.
So, the next time your thoughts spiral out of control—or you jump into something too quickly—don’t beat yourself up. It’s your brain doing its job. And with the right tools, you can train it to work not just faster or slower—but better.
If the science behind overthinking and impulsivity intrigued you, take the next step by exploring how the brain and body work at every level. Start with the Foundation in Science and progress into the Bachelor of Biomedical Science—where you’ll uncover how biology shapes human behaviour, health, and decision-making.
