Dopamine and Traction between Internal and External Time

If dopamine facilitates connection and over-production of dopamine makes events seems to run together, then dopamine’s underproduction generates a more choppy experience. On the other end of the dopamine spectrum from schizophrenia’s over-production, dopamine deficit is tied to the shaking and jerky movements of Parkinson’s disease, and the abrupt attention shifts of Attention Deficit Hyperactivity Disorder (ADHD). In fact, drugs that block dopamine in order to treat schizophrenia or amphetamine overdose can cause Parkinson’s like symptoms in long-term users.[1]

In the extreme case, without any dopamine, distinction and connection both vanish. Time does not pass. The absence of dopamine is the root of the extremely slowed or frozen states of patients described by neurologist Oliver Sacks in his book Awakenings. By administering large doses of the dopamine-mimicking drug L-Dopa, Sacks restored these catatonic patients’ ability to move, participate in the world, describe their experience, and sometimes launched them into hyperactivity. Patients did not report feeling as if they had spent a long time in their frozen state, but instead experienced a sort of timelessness, without perceiving the external motion buzzing around them.[2] One patient described her experience as, “sharp-edges, flat, and geometric, with a quality like a mosaic or stained glass window; there is no sense of space or time as such. Sometimes these ‘stills’ for a flickering vision, like a movie-film which is running too slow.”[2.5]

This is similar to how I would suspect that a photon, in its timeless state, would perceive the world, as frozen. Its interior temporal indivisibility prevents the perception of external divisibility.

Some patients were not completely frozen, but simply moved at imperceptible speeds. Sacks encountered a man in the hallway with who held his hand frozen in midair, for what seemed like hours. L-dopa treatment, enabled the man to explain that he was merely wiping his nose. And sure enough, with the help of time-lapse photography, Sacks was able to see that this man was actually performing such a task, just at imperceptibly slow rates.

Dopamine synthesis and receptors naturally decrease with age. Older people also tend to think time passes more quickly than it does. When asked to estimate when 3 minutes had elapsed, 60-somethings guessed three minutes had elapsed when in fact it had been 3 minutes and 40 seconds, as compared to 20-somethings who were accurate within 3 seconds.[3] Aging’s dopamine decrease, likely accentuates the slowing of one’s internal clock that accompanies a slowing metabolism, and the apparent shortening of years once one has accumulated many to compare them against. The combination of these factors contributes to the apparent increase in the pace of external time that occurs with age. Natural dopamine decline may also play a role in increased learning difficulty and forgetfulness, perhaps due to inattention due to repetition. Or perhaps the dopamine decline is a result of cultivating an increasingly predictable life as one ages rather than continuing to seek out novelty.

In a related but different scenario, ADHD is also associated with decreased dopamine levels, as well as decreased activity in the frontal lobe, basal ganglia, and cerebellum. These are all key for temporal perception. Their decrease manifests as impaired time estimation and a quicker internal sense of time, hence ease of boredom, short attentions spans, and hyperactivity.

David Gilden, a psychologist with a doctorate in astronomy, suggests that people with ADHD actually have a quicker sense of internal time which makes the external world seem to pass more slowly, hence ease of boredom.[4] One way Gilden looks at a sense of internal time is to see how long a person can maintain a rhythm once a metronome is turned off. Apparently 40 beats per minute, or about 1.5 s between beats or .67 Hz, is about as low as most people can go and still maintain an accurate rhythm, just below a leisurely walking pace of about 49 steps per minute. People with ADHD do fine at 60 beats per minute, but cannot sustain the rhythmic feel at 40 beats per minute, suggesting that their internal pacing may be quicker than normal, making it more difficult to connect beats a second and a half apart in time.[5]

At first, neuroscientist Warren Meck thought that the basal ganglia’s neuronal loop was something of an internal clock because of its activation during temporal processing. Meck first postulated that the rate at which signals traverse this loop offers the brain a time keeping mechanism.

Recall, that increased dopamine increases the rate of the basal ganglia loop cycling, forging connections between disparate parts of the brain. This would seem to suggest that more dopamine and a faster internal clock would be associated with a slower perception of external time, like the increases in body temperature. Then lower levels of dopamine and a slower rate of neural circuit frequency might correspond to a slower internal clock and a perceived acceleration of external time. The association however is not so clear-cut. The under- or over-activity of the dopamine system is linked with impairment in accurate time estimation, sometimes making it seem slower, sometimes faster. There is no obvious correlation between perceived speed of time and the amount of dopamine present as one might suspect.[6]

Alternately, neuroscientist Donald Woodward proposes that the basal ganglia loop provides focus, and sometimes it focuses on time, making dopamine more of a clock-watcher than a clock itself. Meck’s studies involved brain scans of people tracking time, so it seems possible that the scans were picking up the neural signature of “tracking” or focus rather than the neural signature “time.”[7] Meck has since incorporated Woodward’s perspective into his theory, recognizing that basal ganglia, with the help of dopamine, seems to track activities of the frontal cortex, possibly deriving its sense of time from the rate of frontal cortex activity.[8]

The brain, of course, has many frequencies cycling at different rates, many, if not all, of which, most likely contribute to one’s experience of time. The ability of the brain to keep all these different frequencies in appropriate relationship to one another, smoothing the flow of connecting thoughts and actions, might be what dopamine helps facilitate. I suggest that dopamine not only encourages the brain to makes connections between internal and external frequencies, but also to bring its own range of frequencies into internal coherence.

As Woodward pointed out, ADHD’s lower levels of dopamine may not be a clear-cut case of the speed of an internal clock, but rather an inability to lock gears between internal and external frequencies. Stripped gears slip and spin. Internal and external asynchronies make it difficult for ADHD folks to gain a sense of traction within themselves and in outer interactions. It may be difficult for them to follow from the beginning to the end of a sentence because they have had 100 divergent thoughts during that time. With decreased dopamine, it is less obvious which thoughts one should pay attention to and which one should suppress.

Alteration in the production and/or utilization of dopamine affects our ability to synchronize our inner experience with external experience. Dopamine says, “Pay attention,” which I suggest, strives to synchronize one’s internal rhythms with external rhythms. Because both internal and external experience consists of so many frequencies this occurs by amplifying an individual frequency signature against the background noise, by paying attention to it.

Multiple frequencies line up when people recognize meaningful stimuli or make decisions, creating an EEG spike, known as P300, that occurs about 300 ms after meaningful stimulus. The spike seems to indicate the constructive amplification of multiple coincident wave crests, the synchronization of several timescales. Memory and present experience align. In ADHD and schizophrenia the amplitude of the P300 indicator decreases, suggesting fewer timescales lining up, more slipping gears.

Continued in “Dopamine, ADHD, and Signal to Noise Ratio”

This is an excerpt from my forthcoming book The Texture of Time.

References:

[1] Chudler, Eric H. Neuroscience for Kids. 2009. Schizophrenia. http://faculty.washington.edu/chudler/schiz.html (accessed Nov. 14, 2009)

[2] Sacks, Oliver. 2004. “Speed.” New Yorker. Aug 23, 2004. p. 60-69

[2.5] (Sacks, 1999, p 19)Sacks, Oliver. 1999. Awakenings. New York: Vintage Books.

[3] Blakeslee S. 1998. “Running late? Researchers blame aging brain”. New York Times. Mar 24, 1998. http://www.nytimes.com/1998/03/24/science/running-late-researchers-blame-aging-brain.html?pagewanted=all&src=pm

[4] Sinn, Jessica. 2011. To the beat of a different drum. University of Texas at Austin. http://www.utexas.edu/features/2011/08/29/adhd/?AddInterest=1283

[5] Gilden, David L., and Laura R. Marusich. 2009. “Contraction of time in attention-deficit hyperactivity disorder.” Neuropsychology 23, no. 2 (2009): 265.

[6] McCrone, John. 1997. When a second lasts forever. In New Scientist Nov 1 1997. http://www.newscientist.com/article/mg15621065.300-when-a-second-lasts-forever—its-not-just-in-the-movies-that-moments-of-crisis-seem-to-pass-in-slow-motion-john-mccrone-investigates-the-tricks-our-minds-play-with-time.html (accessed July 31, 2009)

[7] ibid.

[8] Williams, Caroline. 2006. Teach your brain to stretch time. In New Scientist Feb 4, 2006.http://www.newscientist.com/article/mg18925371.700-teach-your-brain-to-stretch-time.html (accessed Nov. 15, 2009)