“We are what we repeatedly do. Excellence, then, is not an act, but a habit.”  This quote, commonly attributed to the Ancient Greek philosopher Aristotle, places good habits at the heart of a life well-lived. But fast-forward 2000 years, and we are still struggling to make good habits stick. Can neuroscience help bridge the gap between our optimistic resolutions and sub-optimal realities?
As it turns out, the neuroscience of habits is a well-established field with plenty of fascinating insights and actionable tips. But before we get into the how, it helps to understand what a habit is.
What is a habit anyway?
According to psychologists and neuroscientists, habits are behaviours that we repeatedly engage in, even when we no longer expect the outcomes to be rewarding . This seems reflective of our everyday experience, whether it be a “good habit” like brushing your teeth or a “bad habit” like endless Instagram scrolling. I’m pretty sure you don’t get a kick out of picking up your toothbrush, and half the time you’re on social media, you’re bored by what you see. But in both cases, you keep doing it anyway. The question is why?
Of course, neither toothbrushing nor compulsive social media use was hardwired into us. All habits start out as goal-directed behaviours which gradually stabilise into seemingly uncontrollable responses to stimuli . Let’s break that down.
When you first started using Instagram, each scroll produced a new supply of visual candy. Like all pleasurable stimuli, beautiful photos or amusing videos cause a spike in dopamine release in a brain region called the striatum .
Figure 1. The striatum can be further divided into the dorsal and ventral striatum, as shown in this figure. The yellow arrows indicate neurons which release dopamine into the striatum. Other dopaminergic pathways and associated regions are also shown. 
This dopamine spike is essential in the early stages of habit formation, because it helps strengthen the connections between other key neurons - specifically, neurons whose coordinated firing underlies the associations you’re forming between a specific action (the upward flick of your thumb) and a rewarding response (an interesting post) . Neuroscientists call this gradual strengthening of neural connections “long-term potentiation” (LTP) . Thanks to LTP, the next time you are itching for some novelty, you know what to do: just open Insta and scroll!
But we all know a habit doesn’t solidify overnight. In your early Instagram days, your behaviour was still goal-directed (i.e. sensitive to reward contingency) . Imagine if when you first tried the app, it kept giving you boring content. You’d quickly stop using it. But there are two reasons why most of us keep Insta scrolling, even when it’s not all that pleasurable anymore: the algorithm keeps rewarding us at random intervals (ie. “interval reward schedules”) and we’ve done the thumb-flick a million times before (leading to what behavioural scientists call “overtraining”). Interval reward schedules and overtraining are the two key processes by which goal-directed behaviour becomes habitual or reward-insensitive . Instead of performing an action because we expect a resultant reward, we perform the action in a seemingly automated response to stimuli . Have you ever picked up your phone to check an important message, only to find your finger clicking on Instagram or Tik Tok as if it had a mind of its own? This happens because you’re associating your phone with the response of opening social media apps; something you “overtrained” yourself to do. Neuroscientists have even identified specific brain circuits thought to underlie this shift from goal-directed to habitual behaviour. Goal-directed actions are mediated by the “associative network”, which includes the medial prefrontal cortex (mPFC), the caudate (in primates) or its rodent equivalent, the dorsal medial striatum (DMS) . However, as goal-directed behaviours become habitual, the associative network seems to cede control to a closely related “sensorimotor network” . This latter network includes loops between sensorimotor cortices and the putamen in primates or the dorsolateral striatum (DLS) in rodents . Although the physiological mechanisms mediating the associative-to-sensorimotor network shifts are still unclear, sensorimotor cortico-striatal loops are thought to be the core neural substrate of habitual behaviour . Difficulties engaging or regulating these loops may explain why it’s so hard to make a good habit stick or to break a bad one.
Figure 2. Schematic illustration showing the shift from the associative network to the sensorimotor network as behaviour goes from being goal-directed to habitual. The involvement of dopamine neurons in both networks is also shown - as mentioned above, dopamine helps strengthen connections between key neurons involved in forming associations. DA, dopamine; DLS, dorsolateral striatum; DMS, dorsomedial striatum; PFC, prefrontal cortex. 
Why are habits so hard to build or break?
So now that you understand the basic neurobiology of habits, let’s take a look at how things can go wrong. Given that habit formation begins as a goal-directed action, any struggle to build a new habit can be broadly attributed to a lack of motivation . I couldn’t bring myself to exercise daily because staying in bed seemed more pleasant, or finishing my uni assignment seemed more important - in other words, other choices had more motivational sway over me. And the key neurotransmitter underlying both motivation and the necessary movement to reach one’s goals is none other than dopamine .
The pieces are starting to fit together. Dopamine is essential for strengthening the neural connections which mediate early-stage habit formation. But without sufficient pleasure or reward associated with a habit you’re trying to form, you’re not going to get the necessary dopamine spike, and those neural connections are going to remain weak. Your desired habitual behaviour is not going to feel like second nature.
Importantly, building a new habit often involves overriding an old one. Going for a run every morning involves overriding my habitual hitting of the snooze button on my alarm - a response so automatic that it is now probably mediated by the sensorimotor cortico-striatal loops described earlier. The activation of these loops can actually be controlled by our prefrontal cortex (PFC), the part of our brain responsible for overcoming impulses and long-term planning . However, engaging the PFC is highly taxing for our brain, and common challenges of modern life such as stress and fatigue have a negative impact on PFC functioning . So if you’re feeling tired or burnt out, it is more likely that you’ll fall back on old habits and have trouble forming new ones.
Figure 3. Schematic illustration showing the prefrontal cortex (indicated by the colored regions) and its role in providing top-down control of attention, thought, action and emotion. Notably, PFC neurons project to the basal ganglia, a subcortical structure which contains the striatal regions involved in the previously mentioned sensorimotor loops thought to underlie habitual actions. 
How can we build better habits more easily?
The good news is, as we now know, behaviours become habitual through overtraining or pure repetition . So the question is: how can we maximise repetitions when trying to build a new habit, despite wavering motivation levels? A recent podcast episode by neuroscientist Andrew Huberman gives us some great actionable tips .
Slot your habit into the optimal time of day
Any new habit that requires a lot of willpower (e.g. reviewing those dreaded flashcards) or energy (e.g. exercise) is probably best done soon after waking up. This is because upon waking, your body produces elevated levels of cortisol, dopamine and norepinephrine (also known as noradrenaline), with levels remaining relatively high for up to 8 hours . These chemical messengers make us more alert, predispose us towards action , and help bolster our PFC activity in overriding any bad habit impulses .
On the other hand, more mellow or intrinsically motivating habits are best scheduled for later in the day, when the previously mentioned neurochemicals start to taper off, and serotonin levels start to rise . Elevated serotonin puts us into a calm and content state . So if you want to start regular journaling, meditation or engage in some artistic or musical pursuits, anytime between 8 to 14 hours after waking is ideal.
Anchor new habits to reliably recurring stimuli
Habits are just deeply ingrained stimulus-response associations . This means you can make habit formation easier by scheduling your desired behaviour after a recurring action that you already engage in, preferably at the same time and place each day. This technique is also known as “habit stacking” , and I can attest to its effectiveness. After years of failing to “find time” for exercise each day, I experimented with doing physical activity after my well-established morning meditation routine. The “ding” from my phone signalling the end of my meditation becomes a reliable stimulus to trigger my response of taking out my pilates mat. Surprisingly, I’ve now kept up my new exercise habit for over a month, and it definitely feels more automatic than ever before! You can even apply the same principle to a habit you want to perform multiple times a day. Why not take three deep breaths each time you see a notification pop up on your phone? This will not only help you develop a regular mindfulness practice, but also weaken your habitual response of immediately checking notifications.
Control your dopamine release
We’ve learnt that dopamine is essential in the early stages of habit formation, or indeed any form of learning . Although it can be hard to find pleasure in daily revision or getting up early to go for a run, enjoyment of the activity itself is not the only way to get a dopamine spike. We can trigger dopamine release “on-demand” simply by reminding ourselves of the reasons why we are engaging in an otherwise unpleasant activity (for example, “By going for this run, I’ll look better and improve my long-term health”) [11, 16]. Another good motivator is to imagine how good you’ll feel after you’ve completed the task. Engaging in these kinds of thoughts both before and during desired habitual behaviour will give you the dopamine boosts to increase the likelihood that you’ll do it all again. Over time, you may even grow to love the challenge or the discomfort!
In summary, habits can be hard, but they are also the foundations of a life well-lived. So think of one habit you’d like to build, and use the neuroscience-backed tips we’ve covered to start making it a part of your daily routine. Your future self will thank you for it!
 Forbes. Thoughts on the Business of Life [Internet]. Forbes.com. 2022 [cited 26 January 2022]. Available from: https://www.forbes.com/quotes/659/
 Wood W, Rünger D. Psychology of Habit. Annual Review of Psychology. 2016;67(1):289-314.
 Telzer E. Dopaminergic reward sensitivity can promote adolescent health: A new perspective on the mechanism of ventral striatum activation. Developmental Cognitive Neuroscience. 2016;17:57-67.
 Dingman M. 2-Minute Neuroscience: Long-Term Potentiation (LTP) [Internet]. Neuroscientifically Challenged. 2022 [cited 26 January 2022]. Available from: https://tinyurl.com/2bz6udjn
 Yin H, Knowlton B. The role of the basal ganglia in habit formation. Nature Reviews Neuroscience. 2006;7(6):464-476.
 Sheeran P, Webb T, Gollwitzer P. The Interplay Between Goal Intentions and Implementation Intentions. Personality and Social Psychology Bulletin. 2005;31(1):87-98.
 Wise R. Dopamine, learning and motivation. Nature Reviews Neuroscience. 2004;5(6):483-494.
 Daw N, Niv Y, Dayan P. Uncertainty-based competition between prefrontal and dorsolateral striatal systems for behavioral control. Nature Neuroscience. 2005;8(12):1704-1711.
 Radenbach C, Reiter A, Engert V, Sjoerds Z, Villringer A, Heinze H et al. The interaction of acute and chronic stress impairs model-based behavioral control. Psychoneuroendocrinology. 2015;53:268-280.
 Arnsten A, Raskind M, Taylor F, Connor D. The effects of stress exposure on prefrontal cortex: Translating basic research into successful treatments for post-traumatic stress disorder. Neurobiology of Stress. 2015;1:89-99.
 Huberman A. The Science of Making & Breaking Habits [Internet]. Huberman Lab. 2022 [cited 26 January 2022]. Available from: https://hubermanlab.com/the-science-of-making-and-breaking-habits/
 Bahtiyar S, Gulmez Karaca K, Henckens M, Roozendaal B. Norepinephrine and glucocorticoid effects on the brain mechanisms underlying memory accuracy and generalization. Molecular and Cellular Neuroscience. 2020;108:103537.
 Tops M, Russo S, Boksem M, Tucker D. Serotonin: Modulator of a drive to withdraw. Brain and Cognition. 2009;71(3):427-436.
 Scott S. Habit Stacking: 97 Small Life Changes That Take Five Minutes or Less. 1st ed. Scotts Valley, CA: CreateSpace Independent Publishing; 2014.
 Balleine B, O'Doherty J. Human and Rodent Homologies in Action Control: Corticostriatal Determinants of Goal-Directed and Habitual Action. Neuropsychopharmacology. 2009;35(1):48-69.
 Liu C, Goel P, Kaeser P. Spatial and temporal scales of dopamine transmission. Nature Reviews Neuroscience. 2021;22(6):345-358.