PDA

View Full Version : How much data and how fast can the spinal cord transmit to your brain?



Wise Young
10-19-2006, 09:53 AM
I bet that most people know how fast jetplanes go (500-600 mph), how fast their cars travel on highways (50-70 mph), and even how fast their internet connections transmits information (1-5 Mbits/sec) but very few people have any clue how fast and how much information their brains and spinal cords transmit. So, before you look at the answer below, vote in the poll above and then look below to see if you are correct.

************************************************** ***************

The fastest large myelinated axons of the spinal cord transmits action potentials (these are the signals that axons transmit) at the rate of 100-110 meters per second (m/sec). Since there are 3600 seconds in an hour, a conduction velocity of 100 m/sec means that the axons are transmitting at 360,000 meters per hour or 360 kilometers per hour (kph), which comes to about 216 miles per hour (mph).

The diameter of axons and myelination affect the speed of transmission. However, smaller myelinated axons that transmit at speeds of 50 m/sec or less. Likewise, there are many unmyelinated axons that transmit at 1 m/sec. Pain information tends to be be conducted by smaller and unmyelinated axons whereas proprioceptive information (touch, muscle position and length, joint angles) are carried by large myelinated axons. Therefore, the range of conduction velocities range from 1-110 m/sec or about 2-236 mph.

In order for calculate how fast sensory information to get from the tip of your toe all the way to your brain, let us assume that the distance is 2 meters. At about 100 meters/sec, the earliest information should arrive in about 0.02 seconds or 20 milliseconds (msec). However, the information carried by unmyelinated axons may take as long as 2 seconds. These calculations assume that there is no synaptic connection between the incoming signals and the brain.

Synapses are connections between neurons. Once an action potential arrives at the end of an axon contacting another neuron, neurotransmitter are released fairly quickly, within a millisecond (msec). However, it may take 5-10 msec for the neurotransmitters to cause the membrane potential change needed to activate an action potential potential in the receiving neuron.

Somatosensory evoked potentials are electrical signals recorded in the brain in response to stimulation of a peripheral nerve. When one stimulates the peripheral nerve in the feet, for example, the posterior tibialis nerve, it usually takes about 35 msec for the signal to reach the brain. This is because there is at least one synapse between the peripheral nerve and the brain.

One would expect children to have shorter latencies or the time between stimulus and arrival of the signal, because they are shorter and have less distance for the signal to transmit. However, it is interesting that young children under age 8 actually have much longer latencies of 50-60 msec for somatosensory evoked potentials, because the spinal tracts may not be fully myelinated.

Finally, how much information can the central nervous system transmit? This is not a trivial question. Action potentials are binary signals in the sense that they are all-or-none. A single action potential can activate the system but it does not carry all that information. Intensity is encoded in the frequency of bursts of action potential that code. Normally, action potentials themselves are at least 1-2 msec in duration. Therefore, the highest frequency bursts are typically no faster than 500 pulses per second or 500 Hertz (Hz) or 0.5 kilobits/second.

Computer generated signals are also binary and coded in bits. Eight bits is a byte and can encode as many as 256 characters. At 500 Hertz, the central nervous system can transmit at best about 60 bytes per second (e.g. 500 bits/second divided by 8 bits). By comparison, your computer communicates at rates of megabits/second or even gigabits/second. Computers can usually transfer data at rates of 1-10 Mbytes/sec or . Even through a telephone modem, computers achieve rates as high as 60 kilobytes per second.

So, a single wire connection can transmit at rates that are easily 1,000-100,000 more information per second than a single axon can. However, the central nervous system makes up for both the slow rate and slow bandwidth of information transmission by having millions of axons. It is estimated that the human spinal cord has about 20 million axons. Thus, the human spinal cord can transmit gibabits/second. At 0.5 kilobits/second, the maximum information transfer rate will be 10 gigabits per second or close to 1 gigabyte/second.

The injured spinal cord, however, conducts information much more slowly and less volume of information. In general, trauma to the spinal cord selectively damages larger myelinated axons. Thus, the average transmission speed may be as low as 10 m/sec. The number of surviving axons may be 10% of normal. Sensations may take a second or more to get to the brain and the volume of information will be 10 times less.

In summary, I believe that the best answer to the above poll is that the spinal cord transmits information at 100 meters/second and can carry as much as 1 gigabyte/second. However, injured spinal cords conduct about 10 times slower and can transmit 10 times less information.

Leif
10-19-2006, 10:30 AM
Anybody drive a car? I believe anybody that has taken a driver licence would know it although some might have forgotten it he he. During driving education when it comes to the total stopping distance we was learned that the reaction time actually adds quite a few metres to the total stopping distance from when we see a hazard until the foot hits the brake and thereby making the total stopping distance a sum of the reaction time and the breaking distance. So if people are just remembering this before they answer two options on your poll will not be valid because if they were, reaction time would not have been a special chapter in driving education I guess. And if I remember correctly here the reaction time is normally in this example between 1-3 seconds including the milliseconds it takes for the eye to lock onto an object.

PS. You should have made the poll public to see who has to return their driving licences :)

Adrian
10-19-2006, 02:14 PM
Any slower than this and adult giraffes would still walk like new-born giraffes

Wise Young
10-20-2006, 07:20 AM
Anybody drive a car? I believe anybody that has taken a driver licence would know it although some might have forgotten it he he. During driving education when it comes to the total stopping distance we was learned that the reaction time actually adds quite a few metres to the total stopping distance from when we see a hazard until the foot hits the brake and thereby making the total stopping distance a sum of the reaction time and the breaking distance. So if people are just remembering this before they answer two options on your poll will not be valid because if they were, reaction time would not have been a special chapter in driving education I guess. And if I remember correctly here the reaction time is normally in this example between 1-3 seconds including the milliseconds it takes for the eye to lock onto an object.

PS. You should have made the poll public to see who has to return their driving licences :)


You are correct that the response time is relatively slow. The issue of response is quite complex. Let me expand on that a bit below. Sensory information arrives in the brain relatively quickly, usually within 20 msec for visual information, 21-35 msec for touch in proximal limbs, and 35-40 msec for touch in a distal limb. Processing time (the neurons need time to integrate information and respond) may take 20-30 msec. Conduction time for motor responses may take another 30-50 msec. This adds to to afferent conduction, processing, and efferent conduction latencies of about 100 msec.

If you ask a person to sit in front of a computer and tap a key as soon as they see a visual signal, there is usually a latency of 190-220 msec. In other words, it takes about 100 msec longer than one would expect. By the way, you can test this fairly simply by asking a friend to catch a 100 Krone bank note if you hold the note between their thumb and index finger placed about midway on the note. Tell them that they can keep the bill if they catch it. According to Galileo's formula, it should take the note about 100 msec to drop 5 cm. A vast majority of people will not be able to catch the bill on time unless they anticipate the drop, particularly if they are standing. However, be careful with small women and teenagers, especially if they are sitting down or if they have brain damage. Some of them may catch the bill.

So, why does it take so long for the body to respond? The answer to this question turns out to be very important for understanding how our motor systems work and is relevant to spinal cord injury. The brain apparently holds back on all motor responses until the cerebellum checks the posture of the body and gives an okay for the motor response to go ahead. The reason for this is simple. Every movement that you make must be compensated for by your posture. For that reason, response times of people are generally faster and more accurate if they are sitting and the movement is constrained to a small part of the body (by the way, for that reason, I have designed our surgical space in the laboratory so that all microscopic surgery is done sitting down). It takes the cerebellum about 100 msec to poll the postural systems and to make sure that the body is prepared for the intended movement.

This postural checking for intended movements is absent from people who have cerebellar damage. For example, when I was at Stanford medical school many years ago, I helped developed a device to assess postural control and response time of children with cerebral palsy and who have a high risk of getting scoliosis. One group of people that I tested had athetoid cerebral palsy. This is a very interesting form of cerebral palsy where the people have spontaneous writhing motions and difficulty in motor control. Many people with athetoid cerebral palsy have above average intelligence. I found that these individuals often had response times of 90-100 msec. They don't have the postural polling correction delay. That is one of the reasons why I suggest that you don't do the bill-dropping trick with sitting children with brain damage. Some may be able to catch the bill every time.

Regarding cars and stopping time... the rule of of thumb is to put one car length between you and the car in front of you for every 10 mph that you are travelling. Ten miles per hour is about 17 kph. At that speed, you are covering about 5 meters/second. If a car length is 5 meters, that means you have about one second to stop within 5 meters. If your reaction time is 200 msec or 0.2 seconds, that gives only 0.8 seconds for the car's brakes to stop the car within the 5 meters. If you are travelling as 20 mph, you are going 10 meters per second, you need to provide at least two car lengths. While it is true that you have a longer distance (10 meters) to stop, if the car in front comes to a sudden stop, you will hit the car in 1 second if you don't brake. And so on.

I have never tested people with spinal cord injury for their response times. However, it would be very interesting to know whether or not paraplegics have faster response time with their hands than normal. This would not be surprising because the person's cerebellum may not have to poll your posture before the movement. Postural polling by the cerebellum may also be disrupted during the first few months after injury and may account for the unsteady posture of people with spinal cord injury. There have been almost no studies of this, to my knowledge. Everybody assumes that the postural instability of people with spinal cord injury is due to inadequate muscle control. I am not so sure.

Wise.

znop
10-21-2006, 02:48 PM
I don't know why I have not visited this forum before, but I love science and it's easier to understand when someone like DR. Young puts complicated language into somewhat layman"s understanding. Thanks as always Dr. Young.
I learned alot.
John
P.S. Dr Young when did Spinewire(Cando) originate? 1995, 96 or 97.
The first web site I remember was Cure Paralyisis Now where I had the fortune or misfortune to butt heads with DA lol.

I was employed at a college computer lab in from 1995-2001 where I was fortunate to browse an "infant" internet at blazing speeds dut to the T-1 line I believe it was called. Of course I pride myself as an original member and had a lot of pride posting promising news for my fellow SCI's. But when you came along,what can I say, I have been following your every word since.
I wish good health and prosperity to you and your family

Wise Young
10-21-2006, 04:15 PM
znop,

Thanks. While we do have a news forum for general health and science articles, it is not the same. There was no dedicated place on this site to discuss non-SCI related science. This forum was put into place just about a week ago and I moved some of the science-related topics from other forums here. I will move more when I have more time to search through the forums. I know, for example, that we have a very large number of discussions concerning stem cell science and evolution, as well as other scientific issues that really don't fit in the care, cure, life, or politics forums.

Regarding the start-date of Spinewire, we had a version of the web site in 1996 based on Filemaker software. If memory serves me correctly, we formed a company called Lifewire and developed the software for Spinewire in 1997. In 1999, Lifewire merged with Cando and from 2000-2001, the site was called Cando. CareCure began on July 25, 2001 about a week after Cando went bellyup and closed the site.

Wise.

zagam
01-08-2013, 11:14 PM
Hawking thinks its in bit/s. Penrose thinks its in qubit/s.

Whole brain simulations (of more compact organisms) often fail, but they could just be inaccurate and system as a whole may still be classical.

Computers are fast (electro magnetic versus salty water). However, for a successful cyborg the interface technology really needs to improve.

We are really just a wet piece of string.

zagam
01-08-2013, 11:30 PM
Anybody drive a car?
Yes, and I did it fast. This illustrates the massive parallel processing that we are doing with our wet piece of string. It also explains the tunnel vision. You filter out what you can not possibly respond to, but you also plan ahead.

For example break well with a metre when going 10s of metres per second.

This control problem is dynamical system that we solve. Classical artificial neural networks can also solve such problems.

airart1
01-09-2013, 12:37 AM
i was an original member of the cando website, it was a great help, it was right after my divorce in 96 and i was trying to cope on my own without my wife, it was a great help, the internet was still mostly dial-up and we first got on when it came out, i believe aol was the main dialup provider......this site has really transformed, and a great source of info on the web......alot of diverse people.....this was really some great info, dr wise, it puts some great perspective on our nerve damage that i had never heard before, nor really thought about........