Functional neuroimaging
From Free net encyclopedia
Functional neuroimaging is the use of neuroimaging technology to measure an aspect of brain function, often with a view to understanding the relationship between activity in certain brain areas and specific mental functions. It is primarily used as a research tool in cognitive neuroscience and neuropsychology.
Common methods include Positron Emission Tomography (PET), Functional Magnetic Resonance Imaging (fMRI), multichannel Electroencephalography (EEG) or Magnetoencephalography (MEG), and Near Infrared Spectroscopic Imaging (NIRSI). PET, fMRI and NIRSI can measure localized changes in cerebral blood flow related to neural activity. These changes are referred to as "activations". Regions of the brain which are activated when a subject performs a particular task may play a role in the neural computations which contribute to the behaviour. For instance, widespread activation of the occipital lobe is typically seen in tasks which involve visual stimulation (compared with tasks that do not). This part of the brain receives signals from the retina and is believed to play a role in visual perception.
MEG and EEG record neuronal activity directly, while PET of fMRI measurements provide more indirect information about neuronal activity.
Traditional "activation studies" focus on determining distributed patterns of brain activity associated with specific tasks. However, we are able to more thoroughly understand brain function by studying the interaction of distinct brain regions, as a great deal of neural processing is performed by an integrated network of several regions of the brain. An active area of neuroimaging research involves examining the functional connectivity of spatially remote brain regions. Functional connectivity analyses allow the characterization of interregional neural interactions during particular cognitive or motor tasks or merely from spontaneous activity during rest. fMRI and PET enable us to create functional connectivity maps of distinct spatial distributions of temporally correlated brain regions called functional networks.
A direct method to measure functional connectivity is to observe how stimulation of one part of the brain will affect other areas. This can be done noninvasively in humans by combining Transcranial magnetic stimulation with one of the neuroimaging tools such as PET, fMRI, or EEG . Massimini et al. (Science, Sept. 30, 2005) used EEG to record how activity spreads from the stimulated site. They reported that in non-REM sleep (REM = Rapid eye movement), although the brain responds vigorously to stimulation, functional connectivity is much attenuated from its level during wakefulness. Thus, during deep sleep, "brain areas do not talk to each other".
Functional neuroimaging studies have to be carefully designed and interpreted with care. Statistical analysis (often using a technique called statistical parametric mapping) is often needed so that the different sources of activation within the brain can be distinguished from one another. This can be particularly challenging when considering processes which are difficult to conceptualise or have no easily definable task associated with them (for example belief and consciousness).
Functional neuroimaging draws on data from many areas other than cognitive neuroscience, including biological sciences (such as neuroanatomy and neurophysiology) and fields such as physics and maths, to further develop and refine the technology.
See also
- neuroimaging
- electroencephalography (EEG)
- EEG topography
- functional magnetic resonance imaging (fMRI)
- FreeSurfer
- magnetoencephalography (MEG)
- positron emission tomography (PET)
- single photon emission computed tomography (SPECT)
- statistical parametric mapping (SPM)
- Transcranial magnetic stimulation (TMS)
- Near infrared spectroscopy imaging (NIRSI)