"I'm locking in." "I need to lock in." "I'm locked." 

"Locked in" is a now ubiquitous phrase used to describe intense focus. To "lock in," as slang, is to focus on whatever task is at hand, whether it's cramming for an exam, or finishing an assignment, for a prolonged and uninterrupted attention span. This reflects the mental state of being in a state of "flow."

Flow is characterized as full-task engagement with low levels of self-referential thinking. In a flow state, you're entirely focused on the task at hand while barely thinking about yourself. It's typically a state associated with people immersed in activities that require skill, often reflective of professional athletes, musicians, chess players, and other individuals engaged in skill-based tasks. 

Researchers have suggested this mental state is linked to the locus coeruleus-norepinephrine (LC-NE) system. The locus coeruleus (LC) is situated in the brainstem and produces norepinephrine (NE), a neurotransmitter that plays a crucial role in maintaining attention, alertness, and regulating the stress response. This system enables the brain to determine what to focus on by adjusting the strength with which brain signals are processed, thereby improving attention and the ability to adapt one's thinking. 

According to the researchers, the brain state behind flow emerges when the LC-NE system achieves sustained focus and engagement. This idea aligns with the belief that performance is optimal at a moderate level of arousal, such as when someone is neither too bored nor too anxious. The authors propose that flow happens when norepinephrine (NE) levels are in the middle. This allows for intense, focused reactions to what is essential in the task and enables the brain to filter out distractions, staying motivated. 

In a flow state, the brain reduces Default Mode Network (DMN) activity, a part of the brain associated with daydreaming, self-reflection, and mind wandering. Simultaneously, the Central Executive Network (CEN), the part of the brain responsible for focus, decision-making, and goal-directed thinking, becomes active. The LC-NE system is crucial for this, as it helps the brain switch from the DMN to the CEN, making it easier to stay focused on the task and ignore distractions. This is supported by the findings of other researchers, who have shown that the LC-NE system helps balance on-task versus off-task thinking by controlling the level of activity in these networks.

Depending on the complexity of the tasks and the potential for reward, the LC-NE system affects the motivation behind the tasks at hand, which helps the brain decide whether the mental effort is worthwhile. Thus, the flow state occurs when you put in a lot of effort, such as cramming to study for a test or giving your all during a game. Moreover, flow is more likely to occur when the task offers you good feedback, which keeps the LC-NE system focused and engaged, helping you stay motivated and absorbed.