Know Your Brain: The Parietal Lobe — Time in Thy Flight

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The passage of time has always been a subject of intrigue for poets and artists, centuries after we’ve developed ways to objectively measure it in seconds and nanoseconds. Sometimes it’s a thief, or sometimes it’s the only thing that heals all wounds. Even though you can gauge what time it is with a quick glimpse at your phone, it never quite seems like its passage is always constant, with minutes feeling like hours, or a fun night quickly melting away into dawn.

We owe our perception of time to a portion of the brain known as the parietal lobe, which comprises one of four major lobes within the cerebral cortex, positioned behind the frontal lobe and the central sulcus fold that keeps them apart. The central sulcus increases the brain’s surface area and cognitive ability, while the frontal lobe is heavily involved in the brain’s production of dopamine. It is the function of the parietal lobe to act as a mediator — processing sensory information signals — like spatial recognition and navigation, the primary receptive area for touch connecting to the brain’s somatosensory cortex which acts as a budgeting system for the brain’s communications with the body, and the dorsal stream of the visual system.

The primary sensory receptors in the skin — those sensitive to pain, touch, and temperature relay information through the thalamus to the brain’s parietal lobe. Both the superior parietal lobule and inferior parietal lobule act like a tape measure, determining the brain’s sense of spatial awareness, using it to draw a mental map of each room you enter. With all of this responsibility, the parietal lobe is something of a wall to the brain, resting just beneath the thin parietal bone at the sides and roof of the cranium.

Our own concept of time, something as seemingly abstract as time itself, seems like it would be heavy lifting for one region of the brain, but you’d be surprised to learn a few of the parietal lobe’s more interesting functions. Along with “touch localization”: the brain’s ability to detect new stimuli when responding to touch, the parietal lobe specializes in “two-point discrimination”: the ability to recognize two separate objects making contact with the skin as different points, even without being able to look, and “graphesthesia”: the ability to recognize writing as it’s applied to the skin, simply by touch, with no reading involved. A structure known as the posterior parietal cortex is known to vision researchers as the dorsal stream of vision, processing both visual signals and signals of touch, and relaying signals to control movement in the arm, hand, and eyes to formulate a rapid response.

Time In a Bottle

You’ve probably heard that time flies when you’re having fun — when an animated dinner party full of lively conversations ends up burning away three or four hours before you know it. Technically it’s not quite accurate. It might be fairer to say that things are a bit more nuanced, and that it actually flies when you’re instead pleasantly surprised by the amount of fun that you’re having.

A trio of researchers from the Weizmann Institute of Science in Israel decided to further explore the factors that contribute to how we experience time — what neurological mechanisms could be behind why we compress and stretch the most prominent episodes of our lives? Their work, published in the journal Nature Neuroscience, suggests that the answer lies in “operant conditioning”: the system in which the brain learns through a system of continuous rewards and punishments. This system sets our expectations for what will happen to us in the not too distant future, and somehow integrates with our perception of time.

The last few decades of research would indicate that the key to understanding how we perceive time lies in the neurotransmitter dopamine. Research over the last few decades has demonstrated the myriad effects that dopamine has on how much time an individual thinks has elapsed in a given time period. An increase, for example, speeds up your internal clock, according to some studies, and makes you believe that much more time has passed than in reality. Other studies have shown that it has a depressing effect, compressing events to make them seem more fleeting, while others show the dopamine has a mixed effect on the perception of time based on context.

What we do know, however, is dopamine’s longtime association with the brain’s reward circuitry. If you receive an unexpected reward, for example, even if it’s finding money unexpectedly or finding out your favorite team won, you experience a dopamine rush and you associate behaviors associated with that moment in time, with the actual reward and keep doing them. In what’s known as a prediction error, you keep repeating those behaviors in the future even if they’re not associated with the reward.

The connection between dopamine and time perception is likely to be more than just coincidence, however, as drugs like methamphetamine and neurological disorders like Parkinson’s have been consistently known to alter the learning process, and both conditions alter the individual’s levels of dopamine. The ability to learn new skills, linking one behavior to its outcome, requires the perception of time, associating one event with another as it happens. What never really happened before this new paper’s authors came along was determining how both reinforcement learning and time perception are integrated in the brain, that was the question authors Drs. Ido Toren, Kristoffer Aberg, and Rony Paz sought to answer.

In their study, the test subjects were given two separate numbers that flashed on a computer screen. Usually the number would be a zero, with another zero appearing just seconds later. The next number would be shown to the participants at varying intervals, and they would have to report which number lasted longer. Sometimes the second number would be a negative or positive integer that appeared randomly. In cases where the number was positive, the participants were awarded with a small amount of money, but if the integer was negative, they would lose money.

Feelings At A Moment’s Notice

These consequences for the game correlated with shifts in how the participants experienced the duration of time between the first and second numbers. The stronger prediction errors coincided with greater distortions of how much time the participants felt had passed.

Prediction errors aren’t necessarily the only factors that affect the perception of time, however. A study published by the Journal of Neuroscience used a simpler approach. Participants were repeatedly exposed to a brief stimulus and subsequently overestimated the duration for which they experienced the stimulus. The researchers attribute this to the neurons responding to shorter periods of sensory touch becoming worn down, giving the ones accustomed to longer durations more influence on how the sensory signals are picked up in the brain. This means that when it comes to your brain, it could mean playing for a crowd — but it only receives information from a few of its bolder critics. After they experienced a long duration of a stimulus, they took subsequent tests where they experienced sensations for shorter intervals, and typically underestimated the duration.

“By changing the context of the stimulus presentation, we can actually manipulate how participants perceive those durations,” said the study’s co-author Dr. Masamichi Hayashi, a cognitive neuroscientist at the National Institute of Information and Communications Technology in Japan. Scans of brain activity in their study indicated an area in the right parietal lobe became active as the subjects experienced the stimulus and tried to recall it.

Both teams looked at different parts of the brain, but observed similar processes taking place, with one feeding the other. Researchers have noted that the brain may have a number of different processes for keeping time, but Hayashi’s study noted the parietal lobe’s connection to the putamen, involved in regulating movement, suggesting that these structures could coordinate to form a more accurate perception of time. The more we understand the brain, the more it becomes clear how much more subjective the brain is than we would care to believe.

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