Final answer:
An overall brain slowdown is indicated by a slower reaction time. This often ties into the decline in cognitive functions due to factors like aging or stress, affecting decision-making and problem-solving abilities.
Step-by-step explanation:
An overall brain slowdown is evident in the way an individual's reaction time or thought processes speed changes. Among the options provided, the one that indicates an overall brain slowdown is b. slower reaction time. This slowdown in cognitive functions can be due to various factors including age, lack of sleep, stress, or certain health issues. For instance, as we age, our cognitive functions commonly decline, leading to slower reaction times and sometimes slower thinking. This can affect activities such as decision-making and problem-solving that require more effort and cognitive energy. In contrast, faster reaction times, faster thinking, and faster talking would usually signify an active and well-functioning brain.