We all have a sense of being early or late, we know when our birthday is coming up, we can even guess pretty well what time it is now, but how does our mind make this happen?
Science has been studying this question intensively for many years, and recent studies have yielded fascinating results. An article in the Summer 2018 Scientific American special edition on Time reviews many of these findings.
The first insight to share has to do with the fact that all of life tracks time. Even single-celled life forms, such as bacteria, have functions that create a steady beat that allows the single cell to vary its function by the time of day or season.
Time has profound impacts on how each of us, how all people, live. There are mechanisms that keep track of daily variations such as when we eat and sleep, there are mechanisms that keep track of the chronology of our lives (when did various events occur, when will they occur), and one of the more important clocks determine how long, if we stay healthy, we will live.
The Circadian Rhythm.
The word circadian comes from two Latin words that mean, approximately (circa) and day (diem). So literally circadian means, about a day.
And that’s what our circadian rhythms deliver, a daily cycle of all sorts of bodily functions that correspond very closely to about a 24 hour period.
The circadian rhythm dictates key daily variations in our body’s various functions, including- when we wake and sleep, blood pressure going up and down, cortisol secretion, body temperature, gene activation sequences, energy use. The daily variation in cortisol secretion explains so much of when we feel sick when we are ill. Cortisol is the body’s natural prednisone, and like prednisone, is a very potent steroid. The body makes 10-20 times as much cortisol around 8AM as around 8PM, every day. This peak is a very, very potent anti-inflammatory agent, and so at 8AM, the body’s inflammations decrease tremendously. That is why when you have a fever, it often dips in the morning; if you have a cough or runny nose, it is better in the morning.
Our lowest body temperature every day is around 4:30 AM, for many highest alertness peaks at 10 AM, best muscle coordination peaks around 2:30 PM, peak muscle strength and heart function at 5PM, every day.
We now know that our circadian rhythm is created by a tiny number of nerve cells, about 20,000 of them, in our hypothalamus, which is near our pituitary gland which sits in between our eyes and a bit back from there into the brain. These neurons are organized into two clumps of 10,000 each, called a suprachiasmatic nucleus (SCN). The chiasm is where the nerves from each eye cross over each other, again between the eyes and a bit back into the brain area.
These cells dictate the hourly variation that creates the daily rhythms of waking, sleeping, and rising and falling blood pressure, energy use, and cortisol production, amongst many other functions. It is the nerves of the SCN that time when melatonin is to be released as we go to sleep.
More recently, science has discovered that clocks made up of cells, like those in the SCN in the brain, exist all over our body. There are similar clumps of cells that operate clocks in various organs, such as the heart and liver, and they each run sequences independently of each other.
So the heart has its daily rhythms, not just its second to second beats. The liver has its own clock, as does the gut. They coordinate, but do not dictate function to each other.
It is thought that jet lag may result from our body scrambling to readjust all our various clocks when we suddenly appear overseas.
By the way, newborns’ clocks are not set for the 24 hour cycle, a major reason that parents lose sleep after birth. It takes about 6 weeks for a newborn to have all its clocks set to our daily timing.
The Stopwatch and Calendar.
The SCN and other organ clocks are charged with keeping track of where we are in a day, defining a day, repeating rhythms that take 24 hours to complete.
But our mind tracks all sorts of time. A great example is the interval timer. This function lets you know how long an interval of interest, say how long you have to catch a ball, when to clap on beat in a song, or how long you have to lounge around in bed.
Studies on how the brain accomplishes keeping track of time have found all roads converge on an intriguing part of our minds, an area not so familiar to many, the basal ganglia.
The word ganglia is plural for ganglion, which is an old Greek word for a lump near a tendon. Even today we use the word ganglion to refer to a round, hard, fluid-filled bump that sits on one of the tendons of our wrist.
But when it comes to brain science, ganglion refers to a lump of nerves, and that lump has everything to do with how those nerves think and operate. In creatures without a brain, lumps of nerves run the show. From that notion of a ganglion came the idea that rather large groupings of nerves in and around our brain are called ganglia.
If you think of the human brain, think about how it needs to connect to the spinal cord. The structures that connect the brain to the spinal cord are in the shape of a funnel with the wide part attached to the brain and the narrow end to the spinal cord, that whole funnel is called the brainstem. At the base of our brain, in front of the brainstem is a rather large lump of nerves, these are the basal ganglia.
The basal ganglia are best known as the place where our movements get their final adjustment. Consider the situation when you go to pick up a carton of milk, sure the carton is full, but it turns out someone drank it all and it’s empty. The moment you lift the carton you know you were wrong, the full carton is empty, but too late, your hand whams it against the top of the frig.
This happens because although it’s your brain that delivers the idea you will be picking up the milk carton, it is the basal ganglia that sets all the muscles in your arm and hand to lift it, just right, smooth, easy, not too much force, not too little force.
It’s the basal ganglia that allow you to pick up a pencil and write with it with fluency, for Lebron to drop a ball in the hoop with a feather touch, for a ballet dancer to hover with grace.
A famous disease of the basal ganglia is Parkinson’s, which makes the basal ganglia fail to give fluency, and our ability to move falters. We can still move, but fluency is lost.
And, it is the immaturity of that fine tuning, in the basal ganglia, in childhood, that we think is responsible for so many children having tics.
But the basal ganglia not only operate our muscles, they play a large role in our excitement and sense of deep pleasure in the world. Two examples from the world of music illustrate. Imagine you are listening to your favorite playlist or album. You are listening to a track you like, but not a huge amount. But the next track is your favorite, every time you hear this track you get goosebumps. As the first track nears an end, your heart races a bit in anticipation, here comes that fabulous phrase of music. At that moment, one part of your basal ganglia is firing like crazy. Then the favorite passage arrives, and as you hear it, your heart shifts gear from excited anticipation to serene and deep joy, that turns out to be due to another part of your basal ganglia firing.
Isn’t it interesting that these pleasures are operated right next to where the place we organize muscle movement occur? And that the pleasures of anticipation and of actual experience are in two different sets of nerves?
With all that in mind, literally, let us learn what is now know about how the basal ganglia keep track of time.
The basal ganglia have a set of cells, not a large number, heavily connected to nerve cells on the surface of the brain, the cerebral cortex. In the cortex, it turns out, reside a set of nerve cells, each of which fire a signal at a constant rate. One cell may fire 10 times a second, another cell 40 times a second. But each of these cells in the cortex fire at their own rate, constantly.
Now, here is where it gets strange and wonderful, amazing really. If something happens that our mind deems important to remember in time, all the neurons constantly firing at an unchanging rate, fire all together, all at once, then go back to their eternal rate. When that happens, that simultaneous firing sends a signal to the key neurons of the basal ganglia. When an interval of interest has passed from that moment, another part of the basal ganglia sends a jolt of dopamine to that part of the basal ganglia keeping track of intervals, and at that moment, that center records where all the regularly firing neurons of the cortex are in their firing since they fired all at once, and voila (!) the brain knows how much time elapsed between the first moment and the second.
Imagine someone throws a ball to you, the cortex cells all fire at once, when it gets launched. Then you catch it, the dopamine surge flashes, and the basal ganglia record the timing of all the timing neurons during that time interval between throw and catch.
Now, forevermore, as long as you have memory, you know how long it took for that ball to get from your friend to you, given where your friend stood, how hard she threw, what the wind was like. Given the same conditions, next time, you’ll know how long you have to catch it.
That information is then sent from the basal ganglia to the memory areas of the main part of the brain, again, the cortex.
It actually makes sense that the timing of muscle actions, like catching, sit right next to the areas that control motion.
It also explains why Parkinson’s and marijuana use, both of which depress dopamine bursts, slow down the clock in the basal ganglia, so that people affected by either tend to underestimate time elapsed by events. And why people using amphetamines, cocaine, or experience adrenaline have this clock speed up, making one overestimate time estimates.
The Ultimate Clock
Every animal lives a finite lifespan- from a day to a century or more, but each species has its own life clock. No one knows exactly how that clock works, but there is no doubt a clock of some sort is at work. It has nothing to do with wear and tear. All our tissues renew their materials, so every 3 weeks for example, we have an entirely new skin.
One theory of the life clock has to do with the tips of each of our chromosomes, called telomeres. When cells divide a telomere is lost, once they are all gone, they can no longer divide. So that could be a clock for life, but the evidence is not yet to the level of proof on that idea.
Another has to do with genes that control the efficiency of the parts of our cells that make our energy, the mitochondria. As time goes on, our mitochondria get leakier, and all the hazards of getting older, really aging, begin to appear. Make our mitochondria nice and airtight, no leaks, and aging will not occur. But what makes them leakier at age 50 than age 3? How does time impose itself here? We do not know.
But there is a clock running each specie’s life span.
- We don’t tend to think of clocks being in our bodies, but clocks are part of every known type of life.
- Even single-celled bacteria vibrate at set frequencies that allow them to track time, and adjust function according to a daily round of variation. This establishes the power of a circadian (“about a day”) clock inside every cell of all life, that this function is essential to life, andgoes back billions of years.
- And so, we humans have a circadian clock, it varies key functions such as temperature, alertness, when we sleep, when we wake, blood pressure, steroid production, on a strict time schedule whose daily variations are constant from day to day across a lifetime. Our circadian clocks can be found in every organ, with the one in the brain the best understood to date. But each organ’s clock tunes that organ to a separate daily rhythm.
- Another clock keeps tracks of intervals, and is located in the basal ganglia, located at the base of the brain. Intricate connections between the basal ganglia and the surface of the brain, the cortex, allow our brain to take a snapshot after key intervals and remember how long they lasted. This allows for a very wide variety of extremely precise muscle activities that require a sense of timing.
- A third type of clock inside very animal and plant, but not in single-celled forms of life, is the clock of our lifespan. It monitors and manages changes that occur across the entire life of the animal or plant, and that will make aging happen at a pace that defines how long one will live. We don’t know exactly where this clock sits or how it works, but it does define our time alive.
We think our bodies are mainly about big visible functions, like hearts beating, kidneys filtering, lungs breathing, minds thinking and feeling, and all that is true, but in addition, life requires at least 3 kinds of time keepers, as we learn more, we are more fascinated!
To your health,
Dr. Arthur Lavin