Home » Data visualization » Spatial-temporal resolution plots for neuroscience methods

Spatial-temporal resolution plots for neuroscience methods

You must have seen these plots before, where the temporal resolution of various methods of probing brain function is plotted along one axis and their spatial resolution on the other. Spatial resolution is often approximated in terms of units of the nervous system (from dendritic spines through neurons and cortical columns all the way to lobes and hemispheres). Similarly, temporal resolution is indicated with easy-to-understand labels, from milliseconds to hours and beyond.

One of the most complete spatial-temporal resolution plots for neuroscience methods. Notice how the spatial resolution of fMRI stretches down to the millimeter, whereas the temporal resolution of EEG reaches the millisecond. The spatial and temporal sampling (or coverage) of each method is depicted by the height and the width of each box, respectively. From Grinvald and Hildesheim, 2004. Reproduced with permission from Nature Publishing Group.

One of the most complete spatial-temporal resolution plots for neuroscience methods. Notice how the spatial resolution of fMRI stretches down to the millimeter, whereas the temporal resolution of EEG reaches the millisecond. The spatial and temporal sampling (or coverage) of each method is depicted by the height and the width of each box, respectively. From Grinvald and Hildesheim, 2004. Reproduced with permission from Nature Publishing Group.

Thus, functional MRI, which can resolve brain activity down to the millimeter and to the second, occupies a different position on the plot than EEG, whose temporal resolution is much more accurate (within the millisecond) but whose spatial resolution is more on the scale of centimeters. The techniques that boast the highest resolution in both space and time are generally more invasive: intracerebral micro-electrode arrays are a prime example.

These plots also present a crucial piece of information when assessing methods: the extent to which they can sample the brain’s function. This is generally done by drawing an area for each technique that depicts the span that it covers in both dimensions. This notion of sampling or coverage is critical given our current understanding of major cerebral functions being subtended by large-scale networks of neurons that link remote areas into cohesive units. Thus, micro-electrodes can resolve individual neurons, but it is practically impossible to record from more than a few small patches of brain at a time.

The same sampling problem applies to time: micro-electrodes can record high-quality brain signals for days to weeks to a few months, but scarring around the implanted material tends to alter the properties of the signals in the very long term. By contrast, there is no a priori technical hurdle to placing the same subject in the fMRI scanner every day for their entire life.

Using a third dimension

In addition to resolution and coverage, some of the plots go further and use a third dimension (pseudo-3D isometric plots or colors) to represent another feature of the method. For instance, Walsh and Cowey illustrate whether a given method allows interfering with the function of the brain; examples include microstimulation and transcranial magnetic stimulation (TMS).

In this plot, a third dimension is used to illustrate whether a given method allows interfering with brain function, instead of recording its correlates. From Walsh and Cowey, 2000. Reproduced with permission from Nature Publishing Group.

In this plot, a third dimension is used to illustrate whether a given method allows interfering with brain function, instead of recording its correlates. From Walsh and Cowey, 2000. Reproduced with permission from Nature Publishing Group.

In another example, Devor and colleagues nicely use color to show how different optical imaging methods are able to penetrate through the thickness of the brain.

Here, color provides an added dimension, encoding the depth to which each technique can penetrate the depth of the brain tissue. NIRS: near-infrared spectroscopy; DCS: diffuse correlation spectroscopy; OISI: optical intrinsic signal imaging; LSCI: laser speckle contrast imaging; OCT: optical coherence tomography. From Devor et al., 2012. Reproduced with permission from Nature Publishing Group.

Here, color provides an added dimension, encoding the depth to which each technique can penetrate the depth of the brain tissue. NIRS: near-infrared spectroscopy; DCS: diffuse correlation spectroscopy; OISI: optical intrinsic signal imaging; LSCI: laser speckle contrast imaging; OCT: optical coherence tomography. From Devor et al., 2012. Reproduced with permission from Nature Publishing Group.

My final example, taken from an article by Mehta and Parasumaran, uses the third dimension to represent how much a given method forces the subject (human, in this case) to remain immobile. Obviously, fMRI and MEG, where the sensors are fixed to heavy machinery, and not attached to the subject’s head as are EEG electrodes of NIRS sensors, ideally require perfect immobility. This is likely to become a fundamental aspect of neuroscience methods, as neuroscience moves further towards more naturalistic, ecologically valid experimental paradigms.

Here, the third dimension represents how much each technique interferes with the subject's ability to move as data are being acquired. From Mehta and Parasuraman, 2013. Published under a Creative Commons Attribution license (CC BY).

Here, the third dimension represents how much each technique interferes with the subject’s ability to move as data are being acquired. From Mehta and Parasuraman, 2013. Published under a Creative Commons Attribution license (CC BY).

To sum up, any given approach to investigating brain function has a number of dimensions that affect its performance and its adequacy to address a particular question. Spatial-temporal resolution plots for neuroscience methods are a good way of representing this complex dimensionality and a nice example of how one well-designed image can transmit a wealth of information.

References

Grinvald, A., & Hildesheim, R. (2004). VSDI: a new era in functional imaging of cortical dynamics Nature Reviews Neuroscience, 5 (11), 874-885 DOI: 10.1038/nrn1536

Walsh, V., & Cowey, A. (2000). Transcranial magnetic stimulation and cognitive neuroscience Nature Reviews Neuroscience, 1 (1), 73-80 DOI: 10.1038/35036239

Devor, A., Sakadžić, S., Srinivasan, V., Yaseen, M., Nizar, K., Saisan, P., Tian, P., Dale, A., Vinogradov, S., Franceschini, M., & Boas, D. (2012). Frontiers in optical imaging of cerebral blood flow and metabolism Journal of Cerebral Blood Flow & Metabolism, 32 (7), 1259-1276 DOI: 10.1038/jcbfm.2011.195

Mehta, R., & Parasuraman, R. (2013). Neuroergonomics: a review of applications to physical and cognitive work Frontiers in Human Neuroscience, 7 DOI: 10.3389/fnhum.2013.00889

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