Posts Tagged ‘Brain Imaging’

Domains of Knowledge

May 20, 2016

Healthymemory has used this phrase in at least one prior blog post and feels it incumbent upon him to elaborate.  Healthyemory has argued that it is science or rather the scientific method that is responsible for the rapid advancement of the species.  However, Healthymemory has also argued that there are other domains of knowledge and that to be stuck in one level of knowledge is to be an intellectual runt.

Perhaps this can best be illustrated by healthymemory’s  academic discipline, psychology.  This is scientific psychology as opposed to clinical or counseling psychology, although those disciplines can and do make use of the scientific method.  Psychological science is practiced in a wide variety of areas.  Let us start at the bottom and work our way up.  At the most molecular level are psychologists who do studies with animals, then take biological assays of the brains to see how the brains changed as the result of learning.  Then there are studies in which electrodes are placed in the brains of animals and research is done to determine which structures accomplish what.  Human brains are studied using EEGs and a variety of brain imaging techniques to examine how the brain functions.  As a result many cognitive psychology programs are renaming themselves as cognitive neuroscience programs.  Then there are studies of human learning, memory, language processing, concept formation, problem solving and so forth.  At the group  level studies are done regarding the interactions among individuals and team performance.  There are also industrial and organizational programs, which study psychological processes in business and industry.  Moreover this listing is not exhaustive.

Each of these areas use scientific methods, but the scientific method needs to be applied differently depending upon the specific area of investigation.  Studying these different areas provides a wide understanding of the scientific method.  Healthy memory’s personal experience working with many scientists and engineers, is that they understand how to do good science in their specific areas, but that this knowledge often does not transfer to other areas of investigation.  This is why healthy memory argues  that scientific psychology is a good major if the goal is to develop a thorough knowledge of the scientific method.

However, Healthymemory argues that if you want to understand people, then literature would be a better method.  Literature increases empathy, the ability to think and feel as others think and feel.  As everyone is different it is best to read literature dealing with as many different people as possible.  This constitutes an important domain of knowledge that is important for interacting with our fellow human beings.

Theater is a related discipline that develops the same strengths.  This is particularly true if one actually gets into acting where the requirement is to be, to think and act like a specific individual.

Then there is music, which involves the sense of hearing.  And music provides enjoyment and access to a wide range of emotional feelings.
Then there is dancing and learning to express oneself through movements of the body.

And there are athletics each with its own domain of athletic skills.

This list could go on and on, and we could discuss and argue as to what activities, areas of knowledge should qualify as domains of knowledge.

Perhaps the simplest cut is between science and the humanities.  Much has been discussed and argued about these two cultures.  The important point is that they exist and they both need to be appreciated. Another domain, which needs to be included, is the spiritual domain.  Religions and beliefs are present in all cultures, and they provide another needed domain of knowledge.



Consciousness Enters the Lab

April 2, 2016

Consciousness Enters the Lab is the First chapter discussed in “Consciousness and the Brain”  Deciphering How the Brain Codes our Thoughts,” which is an outstanding book by the French neuroscientist Stanislas Dehaene who is the Chair of Experimental Psychology at the College of France.  As was discussed in the previous post, although consciousness is an extremely important concept, it has been difficult to bring it into the lab and conduct meaningful experiments regarding it.  This first chapter discusses the new methodology.

This first chapter focuses on the issue of conscious access, the question being why some of our sensations turn into concept perceptions, while others remain unconscious.  The methodology builds upon one of the oldest in psychophysics, the identification of thresholds.  This involved presenting a stimulus and asking the respondent if it can be perceived.  Brain imaging is then added to this technology to see what parts of the brain are responding.  The signature of consciousness is found in those parts of the brain that respond when the individual indicates the presence of the stimulus.  Parts of the brain will also be responding when the individual does not indicate the presence of the stimulus.  These are the parts of the brain that, although they are activated, do not result in conscious perception.  Remember that most of the brain’s activity is unconscious.  Conscious activity represents only a very small percentage of the brain’s activity, but the parts of the brain that do respond with the individual’s indication that the stimulus is perceived, are those parts that are conscious.  This procedure was invented/discovered  by the late Nobel Prize winner Francis Crick and the neurobiologist Christof Koch.

The procedure is not as simple as it appears.  The identification of a reliable threshold requires multiple trials.  This procedure is also done with multiple participants.  So there are many brain images over many participants.  But when done properly, reliable signatures of conscious activity are identified for the relevant parts of the brain.  Thus, consciousness becomes  a meaningful measure for scientific study.

Scientists have often referred to consciousness as “wakefulness” or “vigilance..”  But wakefulness refers primarily to the sleep-wake cycle. And vigilance refers to the level of excitement in the cortical and thalamic networks that support conscious states.  However, both concepts differ sharply from conscious access.  Wakefulness, vigilance, and attention are enabling conditions for conscious access.  Selective attention and conscious access are also distinct processes.  In many cases attention operates sub rosa, covertly amplifying or squashing incoming information even though the final outcome never makes it into our awareness.

Of course, scientists are creative and there are variants on the above technique.  But the primary point has been made.  We are remain unaware of the vast majority of the activity in the brain.  However, signatures can be developed to identify parts of the brain that reflect conscious activity.


April 18, 2015

Our beliefs direct our lives and how we think.  The initial part of this post comes from an American Scientist (4 April 2015, 28-33) article by Graham Lawton.

Initially our beliefs are determined by default.  Children believe what they are told.  This is fortunate, otherwise the child’s development would be retarded.  So our brains are credulous.  A brain imaging study by Sam Harris illustrated how our brain responds to belief.  People were put in a brain scanner and asked whether the believed in various written statements.   Statements that people believed in produced little characteristic brain activity, just a few flickers in regions associated with reasoning and emotional reward.  However, disbelief  produced longer and stronger activation in regions associated with deliberation and decision making.  Apparently it takes the brain longer to reach a state of disbelief.  Statements that were not believed also activated regions associated  with emotion such as pain and disgust.  These responses make sense when regarded from an evolutionary perspective.

There is also a feeling of rightness that accompanies our beliefs.  This makes evolutionary sense except in the case of delusional beliefs.  People suffering from mental illness can feel quite strongly about delusional beliefs.  And when we here a belief from a friend or acquaintance we find to be incredulous, we might ask, “Are you out of your mind?”

So a reasonable question is where does this feel in of rightness originate.  One is our evolved biology, that has already been discussed.   Another is personal biology.  The case of mental illness has already been mentioned, but there are less extreme examples that researchers have found.  For example, conservatives generally react more fearfully than liberals to frightening images as reflected in measures of arousal such as skin conductance and eye-blink rate.

Of course, the society we keep influences both what we believe and the feeling of rightness.  We tend to associate with like minded people and this has a reinforcing effect on our beliefs.

The problem with beliefs is that progress depends on the questioning of beliefs.  The development and advancement of science depended on questioning not only religious beliefs, but the adequacy of these beliefs.  Progress in the political arena depended on questioning the validity of the concepts of royalty and privileged positions.

Beliefs are a good default position.  Absent beliefs, it would be both difficult and uncomfortable to live.  Nevertheless, beliefs should be challenged when they are clearly incorrect or when they are having undesired consequences,

My personal belief about beliefs is that we manage to live on the basis of internal models we develop about the world.  But I don’t believe that any of my beliefs are certain.  They are weighted with probabilities that can change as the result of new information (data) or as the result of new thinking and reasoning.  Even my most strongly held beliefs are still hedged with some small degree of uncertainty.

A good example of this is Pascal’s argument for believing in God.  His argument was that the payoff for not believing in God could be extremely painful.  However, even if one’s belief was infinitesimally small, one should believe.  I have always found this to be one of the few philosophical arguments to be compelling.  So I believe in God.  Anyone who does believe in God has the comfort of this belief while living.  And if there is no God, one will be dead and have no means of knowing that one was wrong.

Richard Dawkins is a brilliant scientist that has made significant contributions to science.  However, he is one of the most outspoken atheists.  Recently he has admitted that he does have some uncertainty and that he is more accurately an agnostic.  However, he argues that he is far enough down on the agnosticism scale to call himself an atheist.  Here we have a stupid argument from a brilliant man.

I find that  many of the problems people have regarding the existence of God stem from religion.  It is important to keep in mind that religions are human institutions and are flawed.  Religions have done much good, but they have also done harm.  Apart from Pascal’s wager, I have a philosophical need for God.  Of course, I realize that my philosophical needs are not necessarily supported by reality.


Ischemic Stroke and Cognitive Function

February 25, 2015

This blog post is largely based on an article by Marina Fernandez-Andujar and eleven others titled, “Remote Thalamic MIcrostructural  Abnormalities Related to Cognitive Function in Ischemic-Stroke Patients,” published in Neuropsychology (2014), 984-996. Ischemic Stroke or Transient Ischemic Attack (TIA) is a brief period of lack of blood flow to an area of the brain.  This impairs the function of brain cells, so a person suffering from TIA develops symptoms of brain function impairment, such as
Weakness of the face and/or arm, and/or leg muscles on one side of the body
Numbness of face and/or arm and/or leg on one side of the body
Inability to understand spoken language
Inability to speak
Unexplained dizziness or vertigo
Loss of vision through one eye
Double vision or blurry vision
These symptoms of a mini stroke/TIA disappear completely within 24 hours.  Nevertheless, it is important to visit an emergency room as soon as possible.  Even if the event occurred a few days ago, medical attention should still be sought.

The thalamus is a midline symmetrical structure of two halves, within the vertebrate brain, situated between the cerebral cortex and the midbrain. Some of its functions are the relaying of sensory and motor signals to the cerebral cortex, and the regulation of consciousness, sleep, and alertness. The two parts of the thalamus surround the third ventricle. It is the main product of the embryonic diencephalon.
The study compared 17 patients who had suffered right hemisphere ischemic stroke three months previously with 17 controls matched for age, sex, and years of education.

In the interest of brevity, technical terms will not be defined and certain details will be omitted. However, this article reports the results of sophisticated brain imaging and contains a wealth of information for the technical specialist.  Stroke patients showed lower fractional anisotropy (FA) values and higher mean diffusivity (MD) values in specific areas of the right thalamus compared with  controls.  In patients, decreased FA values were associated with lower verbal fluency performance in the right thalamus, and the left thalamus after adjusting for diabetes mellitus.  Increased MD values were associated with lower verbal fluency performance in the right hemisphere after adjusting for diabetes mellitus. The FA and MD values were not related to any cognitive function in the control participants.

Alzheimer’s research has been largely focused on neurofibrillary tangles and amyloid plaques in spite of autopsies indicating the presence of these abnormalities, but not cognitive or behavioral of Alzheimer’s symptoms during the lifetimes of these individuals.  It is important to be aware that dementia can also result from ischemic strokes or Type II diabetes mellitus.

How the Illusion of the Present is Created

January 20, 2015

This blog post is based in large part on an article in New Scientist (10 January 2015, 28-31) by Laura Spinney. Although we feel like we are living in the present, we need to construct the present from what has happened in the recent past. First of all, we need to work with data processed by our senses. Different senses process information at different rates. For example, the auditory system can distinguish two sounds just 2 milliseconds apart, whereas the visual system requires tens of milliseconds. It takes even longer to detect the order of stimuli. There is evidence that even at the subconscious millisecond level, our brains make predictions. For example, when we watch a badly dubbed movie, our brains predict that the audio and visual streams should occur simultaneously, but if the lag between them does not exceed 200 milliseconds we stop noticing that the lip movements and voices of the actors are out of synch. Our brains need to blend these different sources of information coming in at different rates into a coherent present, so we can deal with what is happening in what appears to be now, but is actually the future.

Marc Wittman of the Institute for Frontier Areas of Psychology and Mental Health in Freiberg, Germany has developed a model of how this process occurs by drawing on a very large mass of psychophysical and neuroscientific data (Frontiers in Integrative Neurosciece, vol. 5, article 66). He believes that there are a hierarchy of nows, each of which forms the building blocks of the next, until the property of flow emerges into an the illusion of the present.

Virginie van Wassenhove and her colleagues at the French Medical Research Agency’s Cognitive Neuroimaging Unit in Gif-sur-Yvette have been investigating how the brain might bind incoming information into a unified functional moment. They exposed people to sequences of bleeps and flashes. Both occurred once per second, but 200 milliseconds out of synch. Brain imaging was used to reveal the electrical activity produced by these two stimuli. This consisted of two distinct brain waves, one in the auditory cortex and the other in the visual cortex, both oscillating at the rate of once per second. At first the two oscillations were out of phase and the research participants experience the light and sound as being out of synch. But later they reported starting to perceive the beeps and flashes as being simultaneous, the auditory oscillation became aligned with the visual image. So our brain seems to physically adjust signals to synchronize events if it thinks that they belong together (Neuroimage, vol 92, 274). So it appears that even at the subconcious level our brains are choosing what it allows into a moment. But according to Whittman this functional moment is not the now of which we are conscious. This comes at the next level of his hierarchy, the “experienced moment.”

This experienced moment seems to last between 2 and 3 seconds. David Melcher and his colleagues at the University of Trento, Italy provided a good demonstration of this moment. They presented research participants with short movie clips in which segments lasting from milliseconds to several seconds that had been subdivided into small chunks that were shuffled randomly before presentation. If the shuffling occurred within a segment of 2.5 seconds, people could still follow the story as if they hadn’t noticed the switches. But the participants became confused if the shuffled window was longer than 2.5 seconds (Plos ONE, vol 9, pe102248). So our brains seem able to integrate into a cohesive, comprehensible whole within a time frame of up to 2.5 seconds. The researchers suggest that this window is the “subjective present,” and exists to allow us to consciously perceive complex sequences of events. Melcher thinks that this window provides a bridging mechanism to compensate for the fact that ourackf brains are always working on outdated information. Our brains process stimuli that impinged on our senses hundreds of milliseconds ago, but it we were to react with that lag we would not function effectively in the world. Melcher goes on “Our sense of now can be viewed as psychological illusion based on the past and a prediction of the near future, and this illusion is calibrated so that it allows us to do amazing things like run, jump, play sports or drive a car.”

Wittman acknowledges that it is not clear how all this works. The biological of the experienced moment has yet to be found, however neuroscientist Georg Northoff set of the University of Ottawa has proposed one possibility in his 2013 book, Unlocking the Brain. He speculated that implicit timing could be related to slow cortical potentials that provide a kind of background electrical activity measurable across the brain’s cortex. Wittman notes that it’s telling that these waves of electrical activity can last several seconds. He also notes that consciousness itself is kind of filter because it focuses our attention on some things to the exclusion of others. It could be influenced by factors such as emotion or memory, it might tag or label a subset of functional moments as belonging together, to create an experienced moment.

What about meditators who say they are “in the now?” It is clear that it is impossible to be “in the now.” But is it possible that although they appear to be fooling themselves, they are actually accomplish something good? Data indicate that the answer is yes. Wittman did research in which meditators were able to maintain one interpretation of an ambiguous figure longer than non-meditators. Meditators also tend to score higher on tests of attention and working memory capacity. Wittman notes, “If you are more aware of what is happening around you, you not only experience more in the present moment, you also have more memory content.” He also notes, “Meditators perceive time to pass more slowly than non-meditators, both in the present and retrospectively.”

The final paragraph of the New Scientist article merits direct quotation. “This suggests that with a bit of effort we are all capable of manipulating our perception now. If meditation expands your now, then as well as expanding your mind, it could also expand your life. So, grab hold of your consciousness and revel in the moment for longer. There’s no time like the present.”

Why People Play Slot Machines

May 13, 2014

Regular readers of the healthymemory blog should know that its author believes that it is foolish to play casino games.  Casino games are structured such that the odds always favor the casino, so although there might be winnings in the short run, there is no way there will be winnings in the long run.  In the case of slot machines, they’re usually set up to for a 10% share of the play.  So if you spend $100 on a slot machine, you are likely to lose $10.
So I was quite pleased to come upon an article in The Economist1  that addressed this topic.  Slot machines are tweaked within the realm of randomness  such that “near wins” of two out of three symbols appear quite often.  The notion is that players are so pepped by “almost” winning that they are stimulated to carry on playing.
Brain imaging techniques were used by Dymond of Swansea University in Britain and his colleagues to try to determine why this is the case.  functional Magnetic Resonance Imaging (fMRI) , which show which part of the brain are especially active at any given moment was one technique.  A second technique was magnetoencephalography (MEG) measure the electrical nature of that activity.   These two techniques enabled the building of a map for each research participant’s brain as she played on a simulated slot machine.
The focus was on the theta response, the electrical activity in the 4-7 Hz range.  Previous research has identified this response to be related to the processing of experiences of winning and losing.  There were two groups in the experiment.  One group consisted of participants addicted to playing slot machines.  A second group consisted of non-gamblers.  All research participants showed high theta responses to wins and low ones to loses.  The responses to near wins showed similar responses with the exception of the right orbitofrontal cortex.  The theta activity in the right orbitofrontal cortex of the gamblers showed spikes of about 32% and 27% in their theta waves for wins and near wins respectively.  Non-gamblers showed similar responses for wins, but only a 13% increase in theta wave activity for near wins.
This provides a good example of where your mind needs to control your brain.  Compulsive gamblers should realize that they are compulsive due to their brain responses and adjust their behaviors accordingly.  They need to realize that they are competing against a machine that has been cleverly designed go make them believe they are going to win, when in reality, they will lose in the end.  In other words, their minds need to overrule their brains.


The Amygdala and the Problem of Reverse Inference

January 18, 2014

This blog post is based on the book Brainwashed: The Seductive Appeal of Mindless Neuroscience by Sally Satel and Scott O. Lillenfeld. Please bear with me as this is just the third post that I’ve written based on a source viewed on my Kindle.

The amygdala is a small region on each side of the brain. So we all should have two amygdalae. They are located in the temporal lobes, one in each hemisphere. In popular reports the amygdala has become almost synonymous with the emotional state of fearfulness. This is true. When you experience fear, the amygdala lights up. I have personal experience with research on the amygdala that I conducted when I was a graduate student. This was back in the days before brain imaging. I surgically implanted electrodes in rats placed under anesthesia so that they would electrically stimulate only their amygdalae. They were deprived of water and when placed in the operant chamber, they immediately started drinking. They received a shock after drinking. When they were placed back into the operant chamber they would not drink even if they were thirsty. However, if an electric current had been sent to the amygdalae when they were shocked the memory of the shock would never have been formed, so they would drink without fear when placed back in the operant chamber.

Although the amygdala is involved in fearfulness, it also responds to things that are unexpected, novel, unfamiliar or exciting. “This probably explains its increased activation when men look at pictures of a Ferrari 360 Modena. The amygdala reacts to photos of faces with menacing expressions, but also to photos of friendly, unfamiliar faces. If fearful faces are expected and happy faces unexpected, the amygdala will respond more strongly to the happy faces. The amygdala also helps register the personal relevance of a stimulus at a given moment. For example, one study revealed that hungry subjects manifested more robust amygdala responses to pictures of food than did their nonhungry counterparts.1

This amygdala example illustrates the problem of reverse inference, which is a problem that plagues the popular media. Reverse inference is the common practice of reasoning backward from the neural activation viewed in an image to subjective experience. The problem is that brain structures rarely perform single tasks, so one-to-one mapping between a given region and a particular mental states is highly prone to error. So “When Jeffrey Goldberg views a picture of Mahmoud Ahmadinejad and his ventral striatum lights up like a menorah, some investigators might think, ‘Well we know that the mental striatum is involved with processing reward, so this subject, with his activated mental striatum is experiencing positive feelings for the dictator’”2 This would be true only if the ventral striatum exclusively processed the experience of pleasure. But novelty can also stimulate the ventral striatum.




What Is fMRI?

January 11, 2014

This blog post is based on the book Brainwashed: The Seductive Appeal of Mindless Neuroscience by Sally Satel and Scott O. Lillenfeld. Please bear with me as this is the first post that I’ve written based on a source viewed on my Kindle.

fMRI is the basis for most of the brain images we see. It stands for Functional Magnetic Magnetic Resonance Imaging. Here is a brief description of how it works. Functional MRI reveals oxygen consumption and regional blood flow in the brain. Blood that is carrying more oxygen has different magnetic properties than blood that has already given up its oxygen to supply neurons. The brain will first be scanned which the participant is resting in the device to establish a baseline level. Then the participant is asked to perform a particular task of interest. The difference between this baseline and the activity when this specific task is being performed is measured and called the BOLD (blood-oxygen level response). The higher the level of oxygenated to deoxygenated blood in a particular area of the brain, the higher the energy consumption in that region. The basic unit of analysis in fMRI is called the voxel, which is a combination of volume and pixel. It is a three dimensional unit.

Subtraction is performed on a voxel by voxel level. Each voxel is then assigned a color depending on the strength of the difference in activation of that individual voxel between the control and experimental conditions. The computer then generates an image highlighting the regions that become more active in one condition relative to the other. By convention, researchers use color gradations to reflect the likelihood that the subtraction was not due to chance. A bright color like yellow might mean that the there is only one chance in a thousand that the differences are due to chance, whereas a darker color like purple might mean that the chances are higher, and that the brain differences were more likely to be attributable to random fluctuations in the data. Finally, the computer filters out background noise and prepares the data to be mapped onto a three-dimensional template of the human brain.

The final brain scan that we see rarely portrays the brain activity of a single person. Instead it almost always represents the averaged results of all participants in the study. Any resemblance between brain scans and photographs is illusory. Photos capture images in real time and space. Functional imaging scans are constructed from information derived from the magnetic properties of blood flowing in the brain. Scans are simply a representation of local activation based on statistical differences in BOLD signals.

Consciousness and the Grandmother Cell

February 27, 2011

The notion of a grandmother cell is that there are specific neurons that represent a specific concept of object, such as your grandmother. Initially this concept was not generally accepted. The primary criticism was that too many cells would be needed to identify each individual face because each orientation, expression, and lighting on the face would be different. Moreover, the appearance of the face would change over time.

However, recent research summarized in a Scientific American Mind article1, not only resurrects the notion of the grandmother cell, but also relates it to the phenomenon of consciousness. This research involves placing electrodes in the brain to measure electrical activity. This procedure is so invasive that it is only justified for medical diagnosis and treatment. Neurons in the medial temporal lobe are the source of many epileptic seizures. This region includes the hippocampus and turns visual and other sensory percepts into memories. Although most neurons respond to categories of objects, a few of the neurons were much more discriminating. One hippocampal neuron responded only to photos of Jennifer Aniston, and not to pictures of other actresses. Moreover, the cell responded to seven different pictures of Jennifer Aniston. They also found cells that responded to images of Mother Theresa, to cute little animals, and to the Pythagorean theorem.

Further research, by a highly creative and painstaking research team, developed a technique for making concepts visible. They took a volunteer patient and recorded from a neuron that responded to images of the actor Josh Brolin (who was in her favorite movie) and to another neuron that fired in response to the scene of Marilyn Monroe standing on a subway grill. The patient looked at a monitor where these two images were superimposed. The activity of the two cells controlled the extent to which she saw Brolin or Monroe in the hybrid image. When the patient focused her thoughts on Brolin, the neuron associated with Brolin fired more strongly. Similarly when the patient focused her thoughts on Monroe, the neuron associated with Monroe fired more strongly. Feedback was arranged such that the more one cell fired relative to the other, the more visible that image became as the competing image faded. The image on the screen kept changing until only Brolin or only Monroe remained on the screen. The patient loved it and felt that she was controlling what she saw, which she was.

We know that we can control what we are thinking about and that corresponding neurons and neural circuits respond. But this is, as far as I know, the first demonstration of this phenomenon. By using and controlling the appropriate memory circuits we are able to build and maintain our minds.

1Koch, C. (2011). Being John Malkovich. Scientific American Mind, March/April, 18-19. 


Protected: Human Memory: A Machine for Time Travel

July 15, 2010


How Can The Brain Be Imaged?

November 20, 2009

Technologies that allow us to view what is going on inside the brain are a fairly new and exciting development. This blog provides a very brief explanation of these techniques. There will be frequent references to this blog in future presentations of brain imaging studies.

One of the first techniques was Positron Emission Tomography (PET). PET imaging requires that a radioactive substance called a radiotracer been injected into the bloodstream. This radiotracer makes its way into the brain. The level of radioactivity is extremely low so that the individual undergoing the imaging is not put at risk. The individual lies down within the PET imaging machine and is asked to perform different tasks. A computer processes the data to produce 2- or 3 – dimensional images. The images show blood flow and oxygen and glucose metabolism in the tissues of the brain. These images reflect the amount of brain activity in the different regions of the brain.

Functional Magnetic Resonance Imaging (fMRI) is a more recent development that does not require the injection of radioisotopes into the blood stream. It is an enhancement of Magnetic Resonance Imaging where the individual lies on a table with her head inside a giant magnet. Protons inside the atoms in the brain align themselves with the magnetic field and are wacked temporarily out of alignment by a pulse of radio waves aimed at the brain. As the protons relax back into alignment again, they emit radio waves that a computer uses to create a brain snapshot. fMRI takes advantage of two more facts about the body: (1) blood contains iron and (2) blood rushes to a specific part of the brain when it is activated. As freshly oxygenated blood zooms into a region, the iron distorts the magnetic field enough for the scanner to pick it up.

Prior to the development of these imaging techniques, researchers were restricted to recording electrical activity in the brain from the scalps of humans. Still much valuable data was obtained and these techniques are still used today. Event-related potentials (ERPs) are electrical waveforms that are elicited by specific sights, sounds, or other stimuli. The P300 is a bump in the electrical waveform that occurs within one-third of a second after a person is exposed to a word or some other external stimulus. This heightened activity reflects the additional processing that the brain devotes to novel, distinctive events. Larger P300s tend to be associated with greater subsequent recall.[1]

[1] Reported in Schacter (1996).  Searching for memory:  the brain, the mind, and the past.    New York:  Basic Books.   p. 55.