Think fast: Speed of thought and perception limited by unified neocortical gateway
BOLD response amplitudes and latencies for the response selection (Experiment 1) and encoding bottleneck (Experiment 3) tasks. (A) Typical participant’s SPM of the conjunction of the AV open contrast and VM open contrast showing aSMFC and IFJ ROIs. (B) Left and right hemisphere insula ROIs. (C-F) Curve-fitted BOLD time courses across frontal brain regions for the AV, VM, and dual-task trials in Experiments 1 (Left) and 3 (Right). (c) PNAS, doi: 10.1073/pnas.110358310
(Medical Xpress) -- Historically, perceptual and response rates when multitasking have been interpreted as being limited by independent bottlenecks. While a more recent view suggests that a common bottleneck might be the cause, experimental evidence for its existence have not been determinative. Recently, however, researchers at Vanderbilt University used time-resolved functional magnetic resonance imaging (fMRI) where both the topography and temporal sequence of cortical activation across brain regions is examined to identify a unified attentional bottleneck a network of regions that apparently limits the speeds at which perceptual encoding and decision-making can occur.
The research, conducted by a team of researchers led by Michael N. Tombu at Vanderbilt Universitys Marois Lab, found that the inferior frontal junction, superior medial frontal cortex, and bilateral insula are directly involved in capacity limited processing. The experimental design utilized three interrelated experiments: The first imaged isolated brain regions involved in response selection; the second imaged the same areas during perceptual encoding and the third tracked decision-making delays caused by concurrent perceptual encoding.
Tombu points to two techniques that were critical to demonstrating the existence of a previously hypothetical unified attentional bottleneck neural structure. Identifying timing differences across conditions was critical to the investigation, and both of the techniques we leveraged relate to measuring timing. Generally speaking, fMRI is known for good spatial resolution and bad temporal resolution. Techniques like the electroencephalogram (EEG) are better known for good temporal precision, but they have bad spatial resolution. In the present study we used an interleaved acquisition to double our temporal resolution in the first experiment.
To do this, Tombu explains, they started half of the trials at the beginning of an fMRI data acquisition and the other half halfway through an acquisition. By acquiring data points at twice the number of locations along the hemodynamic response function, a better defined HRF can be established, effectively doubling the temporal resolution of the experiment.
Secondly, Tombu and his colleagues improved temporal resolution by restricting spatial coverage to regions identified in the first experiment and using these savings to increase the temporal resolution of the acquisitions in the second and third experiments. This really let us get a good picture of the relative timings of neural events in those later experiments with decent spatial resolution, which was crucial to resolving the questions we wanted to answer.
Almost all current fMRI research uses blood-oxygen-level dependence (BOLD) the MRI contrast of blood deoxyhemoglobin, or oxygen desaturation as the method for specifying where activity occurs in the brain as the result of various experiences, and the current research was no exception. The team used BOLD to determine where brain activity occurred as subjects where engaged in perception and response while multitasking. Some researchers question BOLD because its signals are relative and not individually quantitative, and so are looking towards other methods of measuring neural activity such as oxygen extraction fraction (OEF) or direct detection of neural current-generated magnetic fields but because the electromagnetic fields created by an active or firing neuron are so weak, the signal-to-noise ratio is extremely low and statistical methods used to extract quantitative data have been largely unsuccessful as of yet. Tombu agrees, pointing out that although you could probably use positron emission tomography (PET) or magnetoencephalogram (MEG) in the present investigation, each has its own drawbacks and advantages and would likely confirm what weve already shown. I think BOLD is a good proxy for neural activity.
That said, Tombu notes, In my opinion there are existing techniques and tools that can be applied to the research questions examined in our paper that provide the next logical steps to better understanding the capacity limitations that dominate human information processing. Specifically, I think that transcranial magnetic stimulation (TMS) will be able to shed some light on the specific roles of different components of the bottleneck network weve identified. Now that we have identified some of the regions that appear to be critical to bottleneck processing, TMS can examine the consequences of deactivating nodes within that network. Neural decoding a technique weve previously used is another technique that can be brought to bear on this problem space.
Tombu adds that Given our focus on timing, any techniques that improve the temporal resolution of the data acquisition would be welcomed.
The resulting fMRI data were analyzed using ANOVA (the ANalysis Of VAriance between groups), says Tombu, primarily to examine timing and amplitude differences across conditions. These analyses were performed largely on fit parameters derived from regions isolated from the statistical parametric maps (SPMs). Although there are alternatives to ANOVA, Tombu points out that in our previous work we used ANOVA, and we wanted to be able to make parallels with that work. Using a different technique would have injecting unnecessary noise into our system. Moreover, my expectation is that our results would have been largely the same using other techniques such as fuzzy clustering or independent component analysis (ICA).
In terms of applications, Tombu says that their research findings answer an outstanding question from the cognitive psychology literature about the existence of a unified bottleneck for memory encoding and response selection. Our results establish that bottleneck processes for both operations are collocated, and in all likelihood also being carried out by the same populations of neurons. This has implications for theory and also leads very naturally to future work that will better define exactly how the brain deals with the problem of limited resources in a world of unlimited possibilities. In the longer term, this may have implications for how computers are designed to deal with exactly the same problem. As we speak, IBM is already developing chips that behave more like neurons in the brain, capable of learning through processes akin to synaptic connections, to develop what the company calls cognitive computing. If we can establish how the brain deals with problems of limited capacity, these principles may also be applied to cognitive computing as well.
Regarding potential medical applications, Tombu notes that numerous disorders relate to attentional deficiencies. Our research speaks directly to the neural mechanisms responsible for the deployment of attention in a range of situations including encoding and response selection. Isolating such a network may help focus research on the potential neural correlates of these disorders.
Taking a larger view, Tombu comments that Work such as that conducted in the present paper using one technique is all well and good and tells us something about how the brain is working, but perhaps its real value is that it informs the field, allowing additional techniques from single cell recording work in non-humans to neuropsychological investigations of abnormal populations to be applied to the same problem.
More information: A Unified attentional bottleneck in the human brain, Published online before print August 8, 2011, doi:10.1073/pnas.1103583108, PNAS August 8, 2011
Copyright 2011 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.
- Brain 'maps' reveal clue to mental decline Feb 08, 2011 | not rated yet | 0
- Neural bottleneck found that thwarts multi-tasking Jan 18, 2007 | not rated yet | 0
- Training can improve multitasking ability Aug 20, 2009 | not rated yet | 0
- Ghosts in the machine: The neural basis of visual illusions in fruit flies Jun 22, 2011 | not rated yet | 0
- Lost in translation: Scientist studies the neural origins of speech disorders Apr 20, 2011 | not rated yet | 0
- Motion perception revisited: High Phi effect challenges established motion perception assumptions Apr 23, 2013 | 3 / 5 (2) | 2
- Anything you can do I can do better: Neuromolecular foundations of the superiority illusion (Update) Apr 02, 2013 | 4.5 / 5 (11) | 5
- The visual system as economist: Neural resource allocation in visual adaptation Mar 30, 2013 | 5 / 5 (2) | 9
- Separate lives: Neuronal and organismal lifespans decoupled Mar 27, 2013 | 4.9 / 5 (8) | 0
- Sizing things up: The evolutionary neurobiology of scale invariance Feb 28, 2013 | 4.8 / 5 (10) | 14
If you became brain-dead, would you want them to pull the plug?
16 hours ago I'd want the rest of me to stay alive. Sure it's a lousy way to live but it beats being all-the-way dead. Maybe if I make it 20 years they'll...
MRI bill question
May 15, 2013 Dear PFers, The hospital gave us a $12k bill for one MRI (head with contrast). The people I talked to at the hospital tell me that they do not...
Ratio of Hydrogen of Oxygen in Dessicated Animal Protein
May 13, 2013 As an experiment, for the past few months I've been consuming at least one portion of Jell-O or unflavored Knox gelatin per day. I'm 64, in very...
Alcohol and acetaminophen
May 13, 2013 Edit: sorry for the typo in the title , can't edit I looked around on google quite a bit and it's very hard to find precise information on the...
Marie Curie's leukemia
May 13, 2013 Does anyone know what might be the cause of Marie Curie's cancer
Genetic variations within and between populations
May 12, 2013 This paper (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1893020/) asserts these two different conclusions: ---Quote--- Thus the answer to the...
- More from Physics Forums - Medical Sciences
More news stories
For combat veterans suffering from post-traumatic stress disorder, 'fear circuitry' in the brain never rests
Chronic trauma can inflict lasting damage to brain regions associated with fear and anxiety. Previous imaging studies of people with post-traumatic stress disorder, or PTSD, have shown that these brain regions can over-or ...
Neuroscience 1 hour ago | not rated yet | 0 |
The neural machinery underlying our olfactory sense continues to be an enigma for neuroscience. A recent review in Neuron seeks to expand traditional ideas about how neurons in the olfactory bulb might encode information about ...
Neuroscience 12 hours ago | not rated yet | 0 |
(Medical Xpress)—What if the quality of your work depends more on your focus on the piano keys or canvas or laptop than your musical or painting or computing skills? If target users can be convinced, they ...
Neuroscience 13 hours ago | 3.7 / 5 (3) | 0 |
Neurological disorders can have a devastating impact on the lives of sufferers and their families.
Neuroscience 18 hours ago | 5 / 5 (1) | 0 |
If you're a left-brain thinker, chances are you use your right hand to hold your cell phone up to your right ear, according to a newly published study from Henry Ford Hospital in Detroit.
Neuroscience May 16, 2013 | 2 / 5 (2) | 0 |
Big names in medicine are set to give an upbeat assessment of the war on AIDS on Tuesday, 30 years after French researchers identified the virus that causes the disease.
40 minutes ago | not rated yet | 0
(AP)—A woman who lost both hands, her left leg and right foot after contracting a flesh-eating disease has been fitted with prosthetic hands.
1 hour ago | not rated yet | 0
In 2008 researchers from the University of Southern Denmark showed that the drug thioridazine, which has previously been used to treat schizophrenia, is also a powerful weapon against antibiotic-resistant bacteria such as ...
10 hours ago | 3.7 / 5 (3) | 0 |
(Medical Xpress)—Working with lab mice models of multiple sclerosis (MS), UC Davis scientists have detected a novel molecular target for the design of drugs that could be safer and more effective than current FDA-approved ...
10 hours ago | 5 / 5 (2) | 0 |
In order to avoid harms associated with alcohol consumption, in 2009 the National Institute on Alcohol Abuse and Alcoholism issued guidelines that define low-risk drinking. These guidelines differ for men and women: no more ...
10 hours ago | not rated yet | 0 |
Treatment for alcohol use disorders works best if the patient actively understands and incorporates the interventions provided in the clinic. Multiple factors can influence both the type and degree of neurocognitive abnormalities ...
10 hours ago | not rated yet | 0 |