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sábado, 3 de marzo de 2012

The Brain's Internal Timer

The Brain's Internal Timer

Have you ever been in this situation? You stop at a red light and wait patiently for it to change to green. As time goes on, you start to think that the light has been red for an unusually long period of time. You look around at other drivers, wondering if they have the same impression, Finally, you decide that the light is malfunctioning and cautiously proceed through the intersection even though the light is still red. What happened?

Maybe you know about your brain's circadian clock, the one that keeps your sleep/wake cycles in tune with the earth's day/night cycle. But did you know there are actually several kinds of clocks in the brain? one of them is an internal timer, much like the wind-up or digital device in your kitchen that you use to remind yourself to take a pizza out of the oven before it burns. this timer is the neurological mechanism that gives your higer brain centers information such as "the light has been red too long," so that you can decide what, if any, action to take.

How the Timer Switches On and Off

The brain's interval timer consists of a network of neurons in the cerebral cortex that fire randomly and independently until something gets their attention (Wright, 2002). When an attention-getting stimulus that has time characteristics (e.g., a traffic light) occurs, the substantia nigra sends out a pulse of dopamine that signals these neurons to fire simultaneously. This simultaneous firing becomes a neurological marker for the beginning of the event. When the event ends, the substantia nigra does the same thing, creating a marker for the end of the event. in some cases, the brain's timer compares its measurements to standards stored in your memory. This is what happens when you are sitting at the traffic light and have the impression that the light has been red too long.

When you concentrate deeply, as happens when you are absorbed in a movie, the timer turns itself off. You find yourself wondering were the time went when you come out of the concentration state. The timer also switches off when you are in an emergency situation or when you are experiencing deep emotions. By contrast, when you are bored, your brain's interval timer alerts you to every passing second, and time seems to creep by.

Accuracy of the Brain's Timer

How accurate is the brain's interval timer? Here's a prime illustration. Your alarm goes off, and you look at the clock. You decide to allow yourself to sleep 10 more minutes. You think of resetting the alarm but decide not because, "I'll wake up," you assure yourself. Remarkably, you wake up again, look at the clock, and note that you have slept for about 10 minutes, just as you planned. but on other occasions, you wake up to find that you have slept for 2 hours rather than 10 minutes. Thus, you have probably learned by experienced that sometimes the brain's timer works well, but at others it fails miserably.

Some of the timer's errors appear to be wired-in (Wright, 2002). one such inherent error is its tendency to underestimate time. Limitations on how many tasks our brains can handle at one time also contribute to the unreliability of the brain's timer. In one study, experimental group participants were instructed to read aloud for a fixed period of time (tracy et al., 1998). Control group subjects did nothing during the period. When the time expired, participants in both groups were asked to estimate how long the interval had been. Experimental group participants gave estimates that were more variable and, on average, much less accurate than those in the control group.

As noted, the substantia nigra and the neurotransmitter dopamine are critical to the operation of the brain's timer. thus, anything that affects either the substantia nigra or dopamine also affects the timer. For example, you may know that Parkinson's disease is associated with dysfunction in the substantia nigra. predictably, researchers have found that individuals who suffer from this condition perform more poorly on tasks involving time estimation than people who don't have the disease (Wright, 2002). Similarly, individuals with schizophrenia, a psychiatric disorder in which dopamine function is impaired, also have difficulty estimating time intervals (Davalos, Kisley, &  Freedman, 2005).

Distortions of time perception are also common among people who use drugs, because, drugs affect the brain's dopamine system. Most drugs give users a sense of expanded time, one minute may seem like an hour (bauer, 2001; Lieving et al., 2006). In one study, when researchers instructed participants to wait for a brief period of time (e.g. 5 seconds) before pressing a lever, marijuana users typically pressed the lever before the specified number of seconds had elapsed, whereas non users were able to accurately estimate short intervals under such conditions (McDonald, Schleifer, Richards, & deWit, 2003).

The Brain's Timer in Every Day Life

Experiences that demonstrate the effects of learning on the brain's timer, such as the traffic light example, suggest that you can exploit the adaptability of the brain's timer to become a better test-taker. By taking practice tests and timing yourself, you can "teach" your brain's timer to more accurately estimate how long it will take you to complete exams of varying lenghts and types. As a result of this improved time-estimation ability, you will be able to make better judgements about pacing yourself during real exams.

However, if you want to spend a few more minutes in dreamland when you wake up on the morning of an exam, don't rely on the brain's timer to wake you up, even if you have practiced doing so. Think in the sleep cycles to understand why. Once you go back to sleep, your brain begins a new sleep cycle, one that will last 90 minutes or so if isn't interrupted. Note that Stage 1, the drowsiness phase, last only a few minutes. If your brain slips into the deeper sleep of Stage 2 before the internal timer wakes you up, you are likely to sleep through the exam. Thus, instead of relying on your brain's internal timer, turn to your alarm clock, one of the many devices humans have invented to compensate for the inaccuracies of our built-in neurological timers.

The World of Psychology p. 150 -1

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