The Limitations Of Lab Experiments
Scientists have learned a great deal about how the brain works from doing EEG and ERP experiments in laboratories. When we do such experiments, we usually measure brain activity when people perform computerized tasks. Such tasks are designed to measure a certain brain function, for example reading words, doing arithmetic, or controlling impulses. Usually, such laboratory tasks are quite different from things that we do in our day-to-day lives.
For example, think about the task with the frequent Xs and rare Os used to study impulse control. Is this the same as controlling your impulses to move around or to chat with another student while your teacher is giving instructions? In the EEG lab, you would be sitting alone, in a quiet room, doing a task like pressing buttons and occasionally trying not to press a button. This lab experiment can tell us some things about how the brain controls impulses, but what does it say about how children deal with their impulses at school? This is a limitation of lab experiments: they measure brain activity in rather unnatural situations .
How Does Eeg Measure Brain Activity
An EEG is a test that detects abnormalities in your brain waves, or in the electrical activity of your brain. During the procedure, electrodes consisting of small metal discs with thin wires are pasted onto your scalp. The electrodes detect tiny electrical charges that result from the activity of your brain cells.
Likewise, how is brain activity measured? Electroencephalography. EEG measures voltage fluctuations resulting from ionic current within the neurons of the brain. Clinically, EEG refers to the recording of the brain’s spontaneous electrical activity over a period of time, as recorded from multiple electrodes placed on the scalp.
Likewise, people ask, what brain waves does an EEG measure?
Theta Waves When measured by an EEG device, these are often referred to as EEG theta waves.
What does slow brain waves on an EEG mean?
Focal slow wave activity on the EEG is indicative of focal cerebral pathology of the underlying brain region. Slowing may be intermittent or persistent, with more persistent or consistently slower activity generally indicating more severe underlying focal cerebral dysfunction.
Functional Magnetic Resonance Imaging
Functional magnetic resonance imaging, or fMRI, might be the most widely known technology for recording neural activity, but it doesnt actually record activity of neurons instead, the multicolour images you see of particular brain regions being lit up reflect blood flow in the brain. More precisely, the signal you see reflects the relative presence of oxygenated versus deoxygenated blood active regions require more oxygenated blood, and so despite being indirect, fMRI allows scientists to infer activity patterns of neurons.
fMRI has become a staple of modern neuroscience research because it allows brain anatomy and function to be correlated in humans. But it does have limitations. Both the spatial and temporal resolutions are poor compared to what wed want a cubic millimetre contains around 60,000 neurons enough to sustain the entire life of a fruit fly or lobster and complex perceptual decisions take only hundreds of milliseconds, but fMRI provides no access to this information.
Nevertheless, fMRI allows an unrivalled look at where and to what extent different functions may be localised within the human brain, and researchers continue to devise ways to improve its spatial and temporal resolution, for example by making the technique sensitive to neuronal changes rather than changes in blood flow. No current technique matches fMRI for its ability to map, or determine the likely source of, cognitive function within the human brain.
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How To Measure Brain Activity For Signs Of Consciousness
Scientists have discovered a new method of communicating with brain damaged patients who appear to be vegetative but are simply unable to respond.
Writing in the Lancet medical journal they describe how they measured electrical activity in the brain to detect consciousness.
The system is portable and they hope it could be used in nursing homes and hospitals to help provide more accurate diagnoses.
Medical correspondent Fergus Walsh met one of the scientists behind the system to discover how it works.
Hacking Your Brain Waves: A Guide To Wearable Meditation Headsets
Perhaps youve seen pictures of people lying in giant machines that record brain activity or a man running on a treadmill with dozens of little wires attached to his muscles.
These devices are usually big, expensive, and operated by people that have been taught how to use them. That could be a thing of the past.
We can now record the same activity using much smaller, inexpensive and easy-to-use wearable technology.
You attach these wearable devices to your body in order to measure physiological activityheart rate, body temperature, respiratory rate, muscle tension, and brain waves.
This is biofeedback. Having immediate feedback from your body can allow you to better understand and react to certain states.
Imagine seeing your brain activity in real-time, while meditating or while feeling stressed at work, and being able to adapt what youre doing to get better results. Or being able to keep track of your heart rate and muscle tension during exercise, to keep an exact measure of how youre improving.
The possibilities are endless, its putting our health and fitness in our own hands, where we can now see and interact with our body in new and exciting ways.
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What Does Fmri Measure
Fig 1. From Kuo, Stokes, Murray & Nobre
When you say brain activity’, many people first think of activity maps generated by functional magnetic resonance imaging . As a non-invasive braining imaging method, fMRI has become the go-to workhorse of cognitive neuroscience. Since the first papers were published in the early 1990s, there has been an explosion of studies using this technique to study brain function, from basic perception to mind-reading for communicating with locked-inpatients or detecting lies in criminal investigations. At its best, fMRI provides unparalleled access to detailed patterns of activity in the healthy human brain at its worst, fMRI could reduce to an expensive generator of 3-dimensional Rorschach images. To understand the relative strengths and weaknesses of fMRI, it is essential to understand exactly what fMRI measures. Without delving too deeply into the nitty-gritty , we will cover the basics that are necessary for understanding the potential and limits of this ever popular and powerful tool.
“fMRI does not directly measure brain activity”
However, fMRI does not exactly measure electrical activity but rather it measures the indirect consequences of neural activity . The pathway from neural activity to the fMRI activity map is schematised in figure 2 below:
Fig 3. From Oxford Sparks
“snapshot is more like a long exposure photograph”
Fig 5. Wiki Commons
“too much data to make sense of”
Confirmatory Tests For Brain Death
Brain death is one of the most serious diagnoses a neurologist can make. Unlike severe forms of coma, a diagnosis of brain death means there is no coming back. Medically, brain death is death.
If the diagnosis is made properly, it can be done just by ensuring the patient is in a coma of a known and irreversible cause, and that certain physical exam findings are absent, including brainstem reflexes and any effort to breathe during an apnea test. The apnea test involves giving the patient oxygen but turning off the ventilator to allow carbon dioxide to build up in the system, which normally triggers an attempt to breathe. There are no well-documented cases of a diagnosis of brain death is carefully made in which the patient then had a meaningful recovery.
However, there are times when meeting all the technical qualifications for brain death is impossible. For example, in severe facial trauma, it may be impossible to perform a reliable examination of the cranial nerves. In some patients, it may be impossible to do an apnea test, either because the patient is too unstable or because they have built up a tolerance for carbon dioxide, as is seen in some patients with a chronic obstructive pulmonary disease or severe sleep apnea. In these cases, additional testing is called for.
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How Does Eeg Work
In EEG, an array of flat metal electrodes are placed on a persons scalp. These electrodes measure electrical signals that result from the activity of neurons in the cerebral cortex. The readings can provide a picture of voltage change on the scalp over time, including at intervals shorter than one second. EEG measures can be used as indicators of mental processes or states and can help diagnose conditions such as epilepsy or a sleep disorder. The record of brain activity produced by EEG is called the electroencephalogram.
Matching Neural Activity To The Bold Signal
Researchers have checked the BOLD signal against both signals from implanted electrodes and signals of field potentials from EEG and MEG. The local field potential, which includes both post-neuron-synaptic activity and internal neuron processing, better predicts the BOLD signal. So the BOLD contrast reflects mainly the inputs to a neuron and the neuron’s integrative processing within its body, and less the output firing of neurons. In humans, electrodes can be implanted only in patients who need surgery as treatment, but evidence suggests a similar relationship at least for the auditory cortex and the primary visual cortex. Activation locations detected by BOLD fMRI in cortical areas are known to tally with CBF-based functional maps from PET scans. Some regions just a few millimeters in size, such as the lateral geniculate nucleus of the thalamus, which relays visual inputs from the retina to the visual cortex, have been shown to generate the BOLD signal correctly when presented with visual input. Nearby regions such as the pulvinar nucleus were not stimulated for this task, indicating millimeter resolution for the spatial extent of the BOLD response, at least in thalamic nuclei. In the rat brain, single-whisker touch has been shown to elicit BOLD signals from the somatosensory cortex.
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What Happens During An Eeg
An EEG may be done on an outpatient basis, or as part of your stay in a hospital. Procedures may vary depending on your condition and your healthcare provider’s practices. Talk with your healthcare provider about what you will experience during your test.
Generally, an EEG procedure follows this process:
Using Portable Eeg In The Classroom
Another aspect of human behavior that is difficult to study in a laboratory is how people interact with one another, for example, the way students interact with each other in school. Laboratory experiments are extremely limited in answering this question, but recent developments in portable EEG now allow scientists to conduct brain research outside of the laboratory.
This is exactly what a team of researchers at New York University did recently . They partnered with a local high school and measured the brain activity of a teacher and a group of students during 11 biology lessons . In each lesson, the students participated in different learning activities, such as lectures, instructional videos, and group discussions. The researchers found that, during these classroom activities, students brain waves were in synchrony. In other words, their brain waves went up and down together, in sync. Even more interestingly, students who reported being more engaged in class were even more in sync with the other students .
- Figure 3 – EEG can be used to measure the brain waves of students in a high school classroom .
- Students brain waves can show high synchrony with other students, which was found for students that were more engaged in class . Low synchrony with other students was found for students who were less engaged.
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Bridging Scales Within The Virtual Brain
Figure 1.3. Multiple scale dimensions in The Virtual Brain .
Graphic representation of scales associated with brain dynamics. The aspects colored with blue underground mark the scales formally represented in TVB. The triangle to the left is a reminder of the lack of clear border between scales. Morphologic level: Lower border of resolution is represented by columns as functional units. Specific cortical-brainstem tracts are currently not established for TVB. Computational basement: As an artificial mathematic level, it is widely represented in TVB and models the whole brain. Structures below the neural masses have no direct representation in TVB. However, microscale features are essential in the development of TVB . Model output: In dependence of the used neural mass model, activity can be represented to the level of neuron populations in the form of subcellular features and from the neuronal scale as spikes, action potentials, oscillations, etc. At the large-scale level, TVB has extensive options representing activity . Empirical measurements: Because of its base the lower threshold of TVB is the resolution of MRI, as also for the network components.
Figure 1.4. Integration of scales within The Virtual Brain via evolution differential equations.
C.R. Mukundan, in, 2013
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Many action potentials combine to form bigger patterns of brain activity. These patterns become thoughts, movements and more. Imagine that those vision neurons detect a mix of colors and edges that look like a baseball, for example. Other networks of neurons may tell the arm to reach out and pick it up. Still other networks may form thoughts about playing catch.
These patterns of thought and movement, combine to form brainwaves. These are overall patterns of the electrical activity happening in the brain at any one time.
Observing the brains electrical activity can help scientists better understand how the brain works. Scientists use a variety of tools to measure action potentials, activity patterns and brainwaves.
Helmets and headbands
The simplest way to study brain activity is to cover the head with a helmet, cap or headband dotted with flat metal sensors. These sensors can pick up electricity inside the brain. A device that graphs that activity is called an EEG, short for electroencephalograph .
An EEG can reveal if someone is awake, asleep or even dreaming. Awake, the brainwaves will look like a bunch of sharp spikes. As someone drifts off to sleep, those spikes will smooth into wavy hills.
Electrodes in the brain
Sensors all over the brain
Magnets for brain mapping
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Evidence For The Importance Of Measuring Total Brain Activity In Neuroimaging
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A principal goal in neuroscience is to understand how neuronal populations across different brain regions process information from the vibrant world, rich in moment-to-moment variations of sight, smell, sound, touch, etc. Traditional inquiries examine how the evoked neuronal responses differ with stimuli . However, the brain detects stimuli reliably even when ambient conditions shift owing to external and/or internal factors. Recent investigations have assessed whether evoked neuronal activity varies when the brain’s operational state is altered, whereby including an independent measure of baseline neuronal activity provides a total measure of neuronal activity for the perturbed state . In PNAS, Li et al. demonstrate in the rat’s olfactory bulb that total bulbar activity level reached upon odor exposure measured by extracellular recordingsis independent of the bulb’s baseline activity level. This result agrees well with previous observations from other cortical sensory systems, using a variety of neuroimaging techniques . Taken together, these studies imply that there may be inherent neuronal mechanisms to ensure a similar level of information transfer from sensory input, regardless of external/internal situations that may impact the brain’s baseline state .
Baseline Versus Activity Conditions
The brain is never completely at rest. It never stops functioning and firing neuronal signals, as well as using oxygen as long as the person in question is alive. In fact, in Stark and Squire’s, 2001 studyWhen zero is not zero: The problem of ambiguous baseline conditions in fMRI, activity in the medial temporal lobe was substantially higher during rest than during several alternative baseline conditions. The effect of this elevated activity during rest was to reduce, eliminate, or even reverse the sign of the activity during task conditions relevant to memory functions. These results demonstrate that periods of rest are associated with significant cognitive activity and are therefore not an optimal baseline for cognition tasks. In order to discern baseline and activation conditions it is necessary to interpret a lot of information. This includes situations as simple as breathing. Periodic blocks may result in identical data of other variance in the data if the person breathes at a regular rate of 1 breath/5sec, and the blocks occur every 10s, thus impairing the data.
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