Spatiotemporal relations of primary sensorimotor and secondary motor activation patterns mapped by NIR imaging

Abstract

Functional near infrared (fNIR) imaging was used to identify spatiotemporal relations between spatially distinct cortical regions activated during various hand and arm motion protocols. Imaging was performed over a field of view (FOV, 12 x 8.4 cm) including the secondary motor, primary sensorimotor, and the posterior parietal cortices over a single brain hemisphere. This is a more extended FOV than typically used in current fNIR studies. Three subjects performed four motor tasks that induced activation over this extended FOV. The tasks included card flipping (pronation and supination) that, to our knowledge, has not been performed in previous functional magnetic resonance imaging (fMRI) or fNIR studies. An earlier rise and a longer duration of the hemodynamic activation response were found in tasks requiring increased physical or mental effort. Additionally, analysis of activation images by cluster component analysis (CCA) demonstrated that cortical regions can be grouped into clusters, which can be adjacent or distant from each other, that have similar temporal activation patterns depending on whether the performed motor task is guided by visual or tactile feedback. These analyses highlight the future potential of fNIR imaging to tackle clinically relevant questions regarding the spatiotemporal relations between different sensorimotor cortex regions, e.g. ones involved in the rehabilitation response to motor impairments.

Keywords: (100.2960) Image analysis; (170.2655) Functional monitoring and imaging; (170.3880) Medical and biological imaging; (300.6340) Spectroscopy, infrared.

Fig. 1

(a) The stand constructed to relieve the subjects from supporting the entire weight of the fibers. In addition, a soft yet sturdy holder was made to hold the fibers in place on top of the subject’s head with good optical contact. (b) Bifurcated fiber bundle source-detector geometry where the ‘X’ symbols are detectors, and the ‘O’ symbols are sources, covering a 12 x 8.4 cm FOV. The encircled areas (black ovals) indicate the short distance source-detector pairs used to detect scalp hemodynamics.

Fig. 2

(a) Flowchart of the algorithm used to remove source-detector pairs with low SNR due to poor optical contact. (b) In time-averaged activation images produced with data from the remaining source-detector pairs [panel (1)], pixel-wise T-tests were performed with corresponding baseline values to identify regions of activation [panel (2)]. Subsequently, source-detector pairs (connected solid circles) were clustered according to their similarity in temporal activation patterns [panel (3); S1/PPC – blue, M1/S1 – red]. Panel (4) shows cluster-averaged time-series data for activation in the M1/S1 region (red curve) and the S1/PPC region (blue curve).

Fig. 3

HbO activation images, having color scales in µMolar, were time-averaged between 5 – 20 s for each task on both visits for all three subjects. The white dashed lines were used to approximately separate the PMC/SMA, M1, S1, and PPC cortical regions, as identified on the far right edge of the figure.

Fig. 4

A time series of HbO activation images for Subject 1, having color scales in µMolar, were time-averaged for every 5 s block over a 30 s period of 15 s stimulation – 15 s rest for a single subject performing all five protocols The white, dashed lines were used to differentiate between the PMC/SMA, M1, S1, and PPC cortical regions, as identified on the far right edge of the figure.

Fig. 5

T-maps and clustered source-detector maps for HbO (left columns) and Hb (right columns) for Subject 1 performing the finger tapping, sensory stimulation, and palm squeezing protocols (rows). The white dashed lines indicate approximate boundaries for the PMC/SMA, M1, S1, and PPC regions. The connected circles in the cluster maps indicate the source-detector pairs that CCA grouped in the same cluster as they had similar time-series activation profiles [Tapping: M1/S1 – red, S1/PPC – blue; Sensory Stimulation: S1/PPC – blue; Palm Squeezing: M1/S1 – red; S1/PPC – blue].

Fig. 6

HbO T-maps and clustered source-detector maps for sequential finger tapping (left columns) and card flipping (right columns) for each Subject (rows). The white dashed lines indicate approximate boundaries for the PMC/SMA, M1, S1, and PPC regions. The connected circles in the cluster maps indicate the source-detector pairs that CCA grouped in the same cluster as they had similar time-series activation profiles [Sequential Tapping: M1 – red, S1/PPC and SMA/PMC – blue; Card Flipping: M1 and SMA/PMC – red, S1/PPC – blue].

Fig. 7

Group analysis T-maps and the clustered fNIR signals for sequential tapping and card flipping. The white dashed lines were used to approximately separate the PMC/SMA, M1, S1, and PPC regions. The connected circles in the cluster maps indicate the source-detector pairs that CCA grouped in the same cluster as they had similar time-series activation profiles [Sequential Tapping: M1/S1 – red, S1/PPC and M1/PMC/SMA – blue; Card Flipping: M1/SMA/PMC – red, S1/PPC - blue.