Tuesday, March 20, 2012

How are brainwaves recorded and viewed on a computer?

One way to do this is to record in-vivo (this is usually done with animals although in some unique cases such as when deep brain stimulation [1]).  This means that you cut a small hole in the skull above the brain area you are interested in and then lower recording electrodes into the brain.

In order to put in the electrodes you use a devise called a stereotaxic which holds the anesthetist animal motionless and allows for precise measurements.

This is a sterotaxic used for rats.

Once in the stereotaxic measurements can be taken from two places depending on which is closer to the intended brain area.  These two areas are called Bregma and Lambda which are intersection points of sutures on the top of the skull.  In literature it is reported that, for example, recording was done -1.5 mm anterior (towards the front of the skull), 0.5 mm lateral (away from the middle of the skull) bregma.

Once electrodes are lowered into the brain the signal is passed through a series of amplifiers and filters (to filter out noise such as the 60 Hz band most electronics give off) to a computer.  There are several programs that can be used to capture and analyze the brain signals.  I use Spike 2 (http://www.ced.co.uk/pru.shtml), another common program is Plexon (http://www.plexon.com/plexon_products.html#Software).

Above is an example of what a brain recording looks like.  This example is of simultaneous recordings from the right and left barrel cortex.  The bottom (x-axis) is time and the left axis has four channels the top two from one electrode in the left barrel cortex and the bottom two from an electrode in the right barrel cortex.  Each signal from an electrode is filtered two different ways in order to see neurons spiking (filters at 250-5000 Hz) and local field potential (LFP) (filtered at 0.1 to 100 Hz)  [2].  The local field potential reflects the voltage in the local extracellular space.

The two periods of blocks you can see in the image are showing the response to stimulation of the rat whisker pad (which projects to the barrel cortex).

On closer inspection (image below) you can see the stimulus and the resulting action potential indicating that a neuron is firing in response to the stimulation.  You can see neuron responding to the stimulus in channels 4 and 8 and the LFP response in channels 5 and 9.

One further step you can take to look at a spiking neuron is to take a Stimulus Trigger Waveform Average (STWA).  This means that you average the neurons response to the stimulus over the entire period it is being stimulated.  In  this case there are 100 stimuli separated by 330 ms (3Hz stimuli for 33.3 s).  This results in:

This is, in a sense, a picture of a neuronal response (a putative pyramidal (exitatory) cell based on the duration of the action potential.)

[1] http://en.wikipedia.org/wiki/Deep_brain_stimulation
[2] http://en.wikipedia.org/wiki/Local_field_potential

Thursday, March 1, 2012

Do women talk more than men?

It turns out that woman really do talk more than men.  2,700 words more a day  in fact.  A study found that on average:

male =  6073 words per day.
female = 8805 words per day.

This makes sense if you think about it based on our hunter gather roots.  Back then men were hunters which relied on stealth and minimal conversation where as women were gathers which allowed for plenty of conversation.

Estimates based on a study that is at the bottom of the linked page:

Wednesday, February 29, 2012

What are some most shocking revelations of human study?

Looking back on human experiments over the years it is often the slightly unethical ones that shed the most light on human nature. Here are a couple of the most interesting:

Milgram’s Experiment:
Stanley Milgram conducted an experiment 1961 looking at human obedience to authority figures. The goal of his experiment was to find out how the German population in world war two could have gone along with Hitler’s ideas and orders. The results of the experiment were shocking.

Milgram experiment on obedience to authority figures:
The experiment consisted of scientist (S) running the experiment, a volunteer participant (W), and a confederate (fake participant that was actually part of the study) (V). Both the participant and the confederate started in a waiting room and drew slips of paper to determine which part of the experiment they would do. This part of the study, however, was fixed. Both slips of paper said teacher and the confederate would pretend that he got the role of the learner.

Once in the experiment the teacher (participant) was put in a separate room from the learner (confederate) and they were able to communicate over an intercom. The teacher would recite a list of words and have the learner recite them back. If the learner got the list wrong the teacher would push a button on a dashboard in front of him that would give the learner a shock. The shocks would get progressively stronger after every wrong answer until they got to a dangerous level as can be seen below.

The learner was a tape recorded dialogue that purposely got a certain amount of answers wrong to see if the teacher would continue to shock them. After a while the learner would start to complain about the shocks, say his heart was hurting, that he had a heart condition, and finally stop responding. The whole time the scientist running the experiment would urge the teacher to continue shocking the learner at higher and higher levels.
Before the experiment Milgram polled people asking how many teachers they thought would go to the maximum voltage. He found that people only thought on average that 1.2% of people would.
Milgram found that 65% (26 of 40) of participants administered the maximum voltage even after the learner had stopped responding. He further found that if there were other confederates in the room with the teacher rooting him on, the percentage rose to around 80%.
This was an incredible result showing how easily people will follow orders from authority even to the point of possibly killing someone.

This is one of the most commonly used examples of an unethical experiment because of the psychological stress it put on the participants.


Stanford Prison Experiment:
Psychology professor Philip Zimbardo at Stanford University created a fake prison on the campus that he intended on having students run and occupy. He had Stanford student volunteer for the study and separated them at random into two groups. One of the groups the guards, the other the inmates.
Very quickly students adapted to their roles:

leading the officers to display authoritarian measures and ultimately to subject some of the prisoners to torture. In turn, many of the prisoners developed passive attitudes and accepted physical abuse, and, at the request of the guards, readily inflicted punishment on other prisoners who attempted to stop it. The experiment even affected Zimbardo himself, who, in his capacity as Prison Superintendent, lost sight of his role as psychologist and permitted the abuse to continue as though it were a real prison. Five of theprisoners were upset enough by the process to quit the experiment early, and the entire experiment was abruptly stopped after only six days. [1]
People’s positions of authority can greatly affect their demeanor and actions.
[1] http://en.wikipedia.org/wiki/Stanford_prison_experiment

This was an answer I wrote on Quora.

What are some things that neuroscientists know but most people don't?

I would say one thing we realize is that we understand relatively little about how the brain functions.  It was only within the last 10 years that we realized the majority of the energy consumption by the brain is not used for conscious response to the outside world (Dark energy [1]).  We discovered the default mode network which is more active during rest and sleep than during attentive states.

The energy consumed by this ever active messaging, known as the brain’s default mode, is about 20 times that used by the  brain when it responds consciously to a pesky fly or another outside stimulus. [2]

[1] http://www.sciencemag.org/content/314/5803/1249.full
[2] http://www.scientificamerican.com/article.cfm?id=the-brains-dark-energy

Neuroscience can explain why so many people believe they have been abducted by aliens. There is a phenomenon called sleep paralysis which is surprisingly common.  In surveys from Canada, China, England, Japan and Nigeria, 20% to 60% of individuals reported having experienced sleep paralysis at least once in their lifetime. [3] Sleep paralysis can occur when you are falling asleep or waking up.  When you are falling asleep the body will go into REM sleep while you are still aware.    You can also become aware before a REM cycle is complete.  The significance of this is that while in REM sleep you are in a state called REM atonia [4] which paralyzes your body so that you do not act out your dreams.  So when people experience sleep paralysis they are conscious but not able to control their body.  Often times this can be accompanied by "hallucinations/dreams" and people will attribute the bizarre experience to an alien abduction.

[3] http://en.wikipedia.org/wiki/Sleep_paralysis
[4] http://en.wikipedia.org/wiki/REM_atonia#Physiology

Body image, the brain can believe that an amputated limb is still there.  This is called the phantom limb and it is very common.  Approximately 60 to 80% of individuals with an amputation experience phantom sensations in their amputated limb, and the majority of the sensations are painful. [5]  This can be a very painful syndrome because the phantom limb will often get stuck in a extremely painful cramped position and the amputee will have no way to stretch the limb and stop the pain.  The phantom limb was essentially untreatable until one neuroscientist, Dr. Ramachandran came up with a remarkably simple treatment.  All he did was make a box with a mirror in it and had the amputee put his intact limb in one side and the amputated limb behind the mirror on the other.  The amputee then moved the intact limb and saw in the mirror his phantom limb moving which tricked his brain into relieving the pain in the phantom limb.  Although the brain is incredibly advanced and "intelligent" it is remarkably easy to trick it.

[5]  http://en.wikipedia.org/wiki/Phantom_limb

This was an answer I wrote on Quora.

What is the sensitivity and frequency range of each human sense?

  •  Vision: visible light goes from 390nm to 750nm. [1]
  • Hearing: audible range of frequencies is from 20Hz to 20,000 Hz. [2]

  • Touch (somatosensory): This begins to get much more difficult to put in terms of bandwidth.  For touch there are 3 different types, movement, pressure, and chemical/temperature. [3]
  • Movement/Pressure (mechanoreceptor): the main thing for this that you can measure in bandwidth is texture (when you are running your finger over a surface for example).  Texture will cause your skin to feel vibrations the main range for those vibrations are from 50 Hz to 300 Hz.
  • Temperature (thermoreceptor): sensitive across all ranges until the nerves die from either the cold or the heat.
  • Smell (olfaction): Its hard to quantify smell as a bandwidth.  However humans have have about 10 cm2 (1.6 sq in) of olfactory epithelium, whereas some dogs have 170 cm2. [4]

  • Taste (gustatory): Very hard to quantify, there are a variety of different types of tastes. [5]

[1] http://en.wikipedia.org/wiki/Visible_spectrum
[2] http://en.wikipedia.org/wiki/Hearing_range

This was an answer I wrote on Quora.

Does the brain consume more calories when we think harder?

Yes the brain does consume more calories when "thinking harder" (more active or engaged).

When your brain is more active, compared to a rest/slow wave sleep state, more of your neurons are firing, and they are firing more often.  When firing they release neurotransmitter (along with several other types of messengers) which then need to be replenished by the neuron.  Creating more neurotransmitters takes energy.  So the more neurotransmitters being released, the more that need to be created, the more calories you are burning.

Interestingly, on average children's brains consume two times as many calories as adult brains do. [1,2]

[1] http://www.dana.org/news/cerebrum/detail.aspx?id=1228

[2] http://www.med.wayne.edu/wayne%20medicine/wm97/brain.htm

This is an answer I wrote on Quora.