Tuesday September 09 2008
Spontaneous brain activity
Researchers from NeuroSpin [1] have established that baseline fluctuations in spontaneous brain activity affect our visual perception. These findings, published in the August 5 issue of the Proceedings of the National Academy of Sciences (PNAS), provide yet another step forward in modeling decision-making, which is one of core focuses in neuroscience today.
Research into brain activity led by functional MRI [2] has revealed that the brain maintains a fluctuating baseline activity, even without stimulus. For instance, even with our eyes closed, and thus free of any visual stimuli, the areas of the brain involved in visual perception display a level of neuronal activity - a level that fluctuates. When analyzing MRI data, these variations in what is known as 'spontaneous' activity are considered as largely negligible background noise, and are thus ignored.
To determine whether these spontaneous fluctuations in the dedicated processing zones of the brain have an impact on perception, the NeuroSpin team ran 12 subjects through fMRI while repeatedly presenting them with an ambiguous snapshot stimulus in brief 150-ms bursts at irregular intervals of at least 20 s. The image used was a two-faced vase (see illustration).
In half of the trials, the subjects perceived the vase, while in the other half they perceived the faces. In-depth analysis of the fMRI data revealed that there was a higher spontaneous neuronal activity in the fusiform face area (FFA), a cortical region preferentially responding to faces, in the trials where subjects had perceived faces instead of a vase. It logically follows that higher pre-stimulus activity in this zone will indicate a greater probability that the subjects will perceive the faces rather than the vase. This makes it possible, by studying a subject's spontaneous neuronal activity, to deduce how they will perceive the stimulus well before it is actually visible.
These findings challenge the whole "behaviorist [3]" vision of brain function. In contrast with a "cognitive black box", the brain is not actually silent or closed off when there is no stimulation and does not simply reflexively respond to outside stimuli. The fluctuations in spontaneous brain activity reveal a dynamic set of intrinsic patterns that never completely stops generating working interpretations of the outside world, thus determining how it interacts constructively with the local environment.
[1]Equipe mixte CEA-I²BM/Inserm
[2]Functional magnetic resonance imaging (fMRI) is an MRI technique geared to studying brain function. fMRI consists in alternating periods of activity (such as moving the fingers of the right hand) with periods of inactivity while running image acquisitions of the whole brain every 1.5 to 6 seconds (which is the average temporal resolution conventionally used in research).
[3]Behaviorism, on a theoretical level, considers that thought operates as a sort of automatic mechanism passively recording data coming in from the surroundings and responding with combinations of reflex actions.
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in ongoing neural activity bias perceptual decisions, PNAS, REF Proc. Natl. Acad. Sci. USA, 105, 10984-10989(2008).[2]Functional magnetic resonance imaging (fMRI) is an MRI technique geared to studying brain function. fMRI consists in alternating periods of activity (such as moving the fingers of the right hand) with periods of inactivity while running image acquisitions of the whole brain every 1.5 to 6 seconds (which is the average temporal resolution conventionally used in research).
[3]Behaviorism, on a theoretical level, considers that thought operates as a sort of automatic mechanism passively recording data coming in from the surroundings and responding with combinations of reflex actions.
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About NeuroSpin:
NeuroSpin, the high-field neuro-imaging facility engineered by the CEA, has been up and running since early 2007. This major facility hopes to peel back the boundaries of very-high-field MRI and pioneer the development of tools, platforms and models capable of furnishing deeper insight and analysis into brain development, brain function, and their concomitant dysfunctions. Boasting a tenfold more powerful spatial and temporal resolution than the instruments currently available, NeuroSpin is a groundbreaking platform for researching the origins of brain disease, tracking therapeutic performance, and engineering surgical strategies. The potential outreach is expected to extend to artificial intelligence, the social sciences, education and industry.
Localized at the CEA's Saclay-based cluster, NeuroSpin is the keystone facility of the Orsay-based Frédéric Joliot Hospital Service (SHFJ), the only imaging platform of its kind in Europe. --------------------------------------
Référence de l’article :
Hesselmann G, Kell C, Eger E, Kleinschmidt A (2008). Spontaneous local variations in ongoing neural activity bias perceptual decisions, PNAS, REF Proc. Natl. Acad. Sci. USA, 105, 10984-10989(2008).
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