How fast is that signal that travels through your neurons? It’s an important question, in part because we are quite literally unaware of the time it takes for it to happen (you were touched on the hand when you felt it, not before). We feel as if we experience the world instantly, react instantly, but we don’t. We feel and react only as quickly as our nervous system can respond.
Later we’ll measure the speed of signals travelling through the nervous system with fancy electrophysiological equipment; here we do it with a meter stick and a stopwatch. We measured how long it took for a squeeze to travel around a ring of people holding hands, then cut out a length of axon (the part of the nerve cell that caries a signal over a long distance) by having the squeeze go to the next person’s shoulder rather than hand. The difference in time between the long loop and the short loop represents the time necessary for the signal to travel through the removed axon.
Our answer: somewhere between 9 and 30 meters per sec (depending on which of our two lab groups you choose to believe). Others have determined the speed in these sensory axons to be on the order of 30 – 75 m/s, so we were pretty close (certainly order of magnitude close).
The fact that signals take time to move around the nervous system has profound implications. We live in the present moment, but the present moment that we experience actually occurred a few fractions of a second earlier. By the time we are consciously aware of something, it’s old news. We are unaware of the delay — it cannot be otherwise. You cannot know that something happened until information about it is processed in your brain; you cannot process information in your brain before that information gets to your brain. There is no possibility of experiencing the world in real time, or for that matter of reacting to the world in real time.
It’s time to get serious about learning. Here are links to a few blog posts that I have written over the past few years in which I offer some guidance to students about how to succeed. I tend to think beyond immediate success in a course; these posts address issues related to doing what you need to do now so that you can get on with your life after college.
And to students who haven’t yet figured this out: professors are here to help you learn. Ask us questions, come to our office hours, view us as your allies in the quest for knowledge. If you want to understand something, we will work hard to make that happen. If you want a good grade we can’t do much for you.
A desire to understand will lead to good grades; a desire for good grades will not lead to understanding.
Blue - original; yellow - copy. Click for entire annotated file.
Albion Alum Cindy (Cardwell) Fast
Here’s a blatant example of plagiarism. gleaned from the interwebs thanks to my friend and former student Cindy Fast. Cindy is a co-author on a recent study that suggests that obesity is a cause rather than a result of laziness. Rats on junk food diets became obese (no surprise) and thereafter were lazier than the control group. Nice study – see a UCLA news release about it here.
As is often the case, internet news sites have picked up on the study – it clearly has some appeal to the general public – and here’s where the fun begins. Cindy noticed a web site that posted an article about the study (as I view it right now the Breaking News at the top of the page says “KATE UPTON POSED IN SEXY BIKINIS AT BOEING-727 WITH ZERO GRAVITY” – clearly a high-quality site). What Cindy also noted was that the article on this www.dailynewsen.com site was essentially identical to the UCLA news release, with some synonyms replacing words from the original. Now I understand that the purpose of a news release is to get the word out about something, and I know that these releases are frequently used verbatim by the media. This case is different it seems to me, because daileynewsen.com modified the release, often butchering the meaning and the English language, presumably to disguise the fact that they simply copied from the news release.
I found their attempt remarkable, and sad, because of its similarity to what I sometimes see in student papers. Many students do not realize that “putting something in your own words” does not mean “substituting synonyms for the words in the original.” Plagiarism detection software is often fooled by this, but a reader with even minimal acumen can detect it quickly without access to the original; sometimes words just seem wrong or out of place when they are substituted in place of someone else’s words.
So, I annotated this, and I post it here, for your education and your viewing pleasure. Students: please understand that you should not simply change the words of someone else’s writing — this does not make it yours. And to those students who have a paper due in my class in two days: make whatever changes are necessary, and quickly (or should I say “and fast”).
P.S. How did Cindy notice the word substitutions? The copying web site substituted a synonym in one of the most obvious places that a co-author whose work is being described might look — they listed her as Cynthia D. Quickly.
Students in the Neurophysiology for Beginners course welcomed Tim Marzullo, co-founder of Backyard Brains, to our lab recently. Tim and his partner Greg Gage founded Backyard Brains to make neuroscience equipment available at low cost, hoping to jump-start the neuro revolution. By putting neuroscience tools in the hands of students earlier in their careers, Backyard Brains hopes to bring more people into neuroscience and thereby increase the number of people working to fix problems with the brain.
In the Summer of 2010 I decided to switch my research focus from mammalian learning to learning in earthworms. The reasons for the decision are still not entirely clear, even to me. Experiments with rats were starting to require more paperwork and approval, slowing the process and making student-drive projects in the time frame of a single semester nearly impossible… Rats are expensive (~$30 each) and money is tight… I felt at a dead-end with regard to my rat studies… Whatever the reason, I wanted a change.
One of my first psychology studies ever (during a 6-week psychology segment in high school – thanks Mr. Bingham!) involved training earthworms to turn left in a T-maze. It worked, sort of – the worms achieved about 70% accuracy, as I recall. This was in 1972 or 1973 – around the time that Rosenkoetter & Boyce were publishing their work showing that T-maze learning research in earthworms was flawed, and essentially putting an end to instrumental learning studies in earthworms. As a poorly-read high-school student, I knew nothing of their work.
Maybe it was a memory of this early study that brought me back to earthworms, but whatever the reason, I made the change.
Many enthusiastic student researchers later (two summer FURSCA students and 11 other students who have contributed to presentations at meeting), the research is clearly paying off. First sign of this was an invitation to present at a symposium in 2011 associated with the Society for Neuroscience meeting in Washington, DC. Now two papers related to my earthworm work have been published:
So what good will come from this line of research? Well, if I’m being really optimistic, I’ll tell you that we’ll gain a better understanding of how learning and memory work at a neural level – not just in earthworms but in humans as well – with implications for cures for memory disorders. If I’m being a bit less optimistic I’ll argue that we’ll increase knowledge about this particular animal, and basic knowledge in and of itself is a good thing. But regardless of my level of optimism, I’ll tell you that the research allows many bright students to become better scientists, developing their research design, data analysis, and laboratory skills. This is enough.
In Neurophysiology for Beginners we used dominoes to explore some of the basic principles of action potentials (all-or-none nature of the signal, temporal coding, etc.). Of course, students couldn’t resist getting creative with them.
Click for gallery of Lytro photos.
And here are some cross-view 3D images; cross your eyes until a fused image appears in the center and it will we 3D, like the old ViewMaster pictures.
Ever wonder what it would be like to be a falcon? Suzanne Amador Kane, a Physics professor at my alma mater (Haverford College) and her student Marjon Zamani have published a paper based on amazing video captured by falcons wearing helmet-cams. I do not want to be the crow.
From the video.
Now if only I could develop a helmet-cam for my earthworms…
Six Albion students in the Neuroscience Concentration attended the 2013 meeting of the Society for Neuroscience in San Diego, CA, November 9 — 13. Two, Melissa Baguzis and Holly Paxton, presented their research done with me on the tendency for the brain to be depicted as if seen from the left side. Four other neuroscience concentrators, Emily Morlock, Megan Nuzzolillo, Chelsea Weiss, and Megan Wickens, attended to learn more about neuroscience.
WIth the leaders of WIL.
In addition to hearing about cutting-edge research in the field, students had two meetings over dinner with successful neuroscientists. We met with four women instrumental in leading a national organization, Women in Learning, whose goal is to provide “advice, support, and guidance on the advancement of female researchers from a notable female researcher who has already carved a path in the field.” Moriel Zelikowsky, who founded WIL, is a post-doctoral researcher at Cal Tech; Marieke Gilmartin is an assistant professor at Marquette University; Sarah Hersman and Jennifer Perusini are graduate students at UCLA. Our students got insight into success in graduate school during our dinner.
With Ki Ann Goosens (MIT)
We also met with Ki Ann Goosens, an assistant professor at MIT. Her research focuses on brain mechanisms of fear, with an eye toward treatments for PTSD. In addition to sharing her perspective on what it takes to succeed in science, Dr. Goosens recounted her experience of nearly being eaten by a pack of lions.
And in what has become a tradition, we met with Albion alums who have gone on in the field and who attended the meeting. This growing group also willingly shared good advice with our students about planning for the future.
I was struck this week by the dedication shown by scientists, and by the initiative that they take to get answers. Most of us recognize motivation as an important attribute of a successful scientist, but few of us realize the lengths to which the motivated scientist will go to achieve his/her goals. This was brought home to me this week as I read Galvani’s Spark: The Story of the Nerve Impulse, a fascinating history of neurophysiology by Alan McComas. Much of the info that I relate here comes from that book; the sense of awe comes from me.
As early as the 1700s people who cared enough to wonder about it came to realize that the signals that travel through nerves must be electrical. But exactly what was the nature of this electrical signal? What did it look like? How quickly did it occur? How fast did it travel? Even the idea that it took any time at all to travel was somewhat revolutionary; the great sensory physiologist Müller (1838) was convinced that nervous signals traveled at something approaching the speed of light, a speed too quick to be measured in his estimation.
Today we know the answers to these questions; in fact if you have $100 and a smart phone or computer you can see a neural signal for yourself. All you need is an amplifier and an oscilloscope; components than can be purchased off-the-shelf from any electronic supplier, from Amazon, or from ebay.
But suppose you lived 100 years ago, or earlier? What was an aspiring neurophysiologist to do? Here’s a hint: that budding scientist had to be skilled in various fields, including electronics, or no science would get done. According to McComas’ account, a rite of passage for the young physiologist in the early 20th century was to build his own amplifier! Yes, that’s right; passing the final in Physiology 101 (or more likely Physiology 499) wasn’t enough. To be successful you had to know enough electronics to build your equipment.
One of the first successful measurements of the nerve impulse was achieved by Bernstein in 1868, well before reliable amplification of the tiny nerve signal was possible. Bernstein needed to deliver very brief pulses of electricity to a nerve, and then record the signals created by the pulse at a very precise time after stimulation. No problem today: adjust the Length of Stimulation dial on your stimulator, allow it to trigger the sweep on your oscilloscope, and you’re set. Bernstein had to invent a device that would both deliver the brief pulse and time the recording: his differential rheotome did just that. A metal pin on the circumference of a wheel spinning at a known rate (simple for clockmakers to achieve) contacted a wire once per revolution, closing a circuit and stimulating a nerve. Elsewhere on the circumference were two leads that would be dipped into a mercury bath once per revolution, allowing the minuscule voltage in the nerve to be recorded. By varying the angle between the stimulating pins and the mercury bath, Bernstein could vary the time between stimulation and recording. Without amplification of the tiny nerve voltage Bernstein had to allow the effects of many stimulations to accumulate in order to be measured, but his rheotome was precise enough that this was not difficult.
Bernstein didn’t simply buy a stimulator and the timing equipment; he envisioned it and built it! And not 30 years after Müller had declared that it would never happen, Bernstein had measured the nerve signal.
Nerve Signal constructed by Bernstein
The difficulty created by the tiny size of the signal disappeared with the invention of the amplifier, but another problem persisted. The nerve spike (its shape was pretty well established by then) happened very quickly, and measuring devices, being physical objects, possessed inertia that had to be overcome. If the nerve spike rises in 1 millisecond (and it does) then a physical object that is slow to start moving and then slow to stop will likely distort the signal. In the early 1900s the cathode ray tube (CRT) had been developed: a beam of electrons (almost, if not totally, inertia-less) could be deflected by electrical fields, changing the spot where it hit a fluorescent screen. If one constantly cycling voltage caused the beam to sweep across the screen at a known rate, and another voltage from the amplified nerve signal moved the beam up and down, the shape of an undistorted nerve signal would be readily apparent.
Gasser and Erlanger, at Washington University, recognized this use of the CRT. All they had to do was get one. Westinghouse wouldn’t sell one of these rare and valuable CRTs to a pair of scientists, so Gasser and Erlanger built their own! Yes – they built a CRT, then used it to build an oscilloscope, then were the first to actually “see” the nerve impulse. I can not imagine even thinking this way: “it would be great to have an oscilloscope, but I can’t buy one, so I’ll build one.”
Fountain's Octagon Chamber for Rule Learning in Rats
On the other hand, maybe I can imagine it. I was attracted to the study of animal behavior in part because of the challenge of measurement. How can I ask a non-verbal animal a question, and understand the answer? This often involves instrumentation not readily available for purchase, or perhaps not even imagined yet by anyone. So learning theorists devise the behavioral equivalents of oscilloscopes and rheotomes to get their answers: Want to study how rats learn and remember rules? Devise a device that allows them to get a reward only if they follow a rule. Interested in short-term memory in the mouse? Invent the radial arm maze. Need to measure a behavioral response in an earthworm? How about a running wheel?
When an inquisitive scientist hits a wall, and can’t find the necessary instrument, s/he invents and builds it. The process of building has gotten easier (Electronic device? Use an Arduino as the base, or simulate it with a computer. Complex 3-D shape? Print it.), but the creative spark is unchanged. The successful scientist today might not need to build her own amplifier or oscilloscope, but in order to succeed she would be ready to do so.
The world doesn’t make it easy, but it rewards persistence and drive.
I realized that there are several posts here that relate to gaining admission to grad school, so I’ve created a page on which I consolidate those posts. (A link also appears in the menu bar above.) As I add other relevant posts I will place a link on that page so that all of these grad-school-related materials can be found more easily than via a search. Feel free to email me (email@example.com) to let me know if my comments are helpful.
And of course, current students are encouraged to come see me at any time to talk about issues related to grad school (or about anything, for that matter).
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