Ocular abnormalities have apparent effects on brain activation. However, neuroimaging data about the ocular characteristics of healthy participants are still lacking to be compared with data for patients with ocular pathology. The objective of this multiple participants’ functional magnetic resonance imaging (fMRI) studies was to investigate the brain activation characteristics of healthy participants when they view stimuli of various shapes, pattern and size. During the fMRI scans, the participants view the growing ring, rotating wedge, flipping hour glass/bow tie, quadrant arc and full checker board stimuli. All stimuli have elements of black-and-white checkerboard pattern. Statistical parametric mapping (SPM) was used in generating brain activation via fixed-effects (FFX) and conjunction analyses. The stimuli of various shapes, pattern and size produce different brain activation with more activation concentrated in the left hemisphere. These results are supported by the conjunction analysis which indicated that the left pre-central, post-central, superior temporal and occipital gyrus as well as the left cingulate cortices were involved when the participants viewed each given stimulus. Differential activation analysis showed activation with high specificity in the occipital region due to the stimuli of various shapes, pattern and size. The activation in the right middle temporal gyrus was found to be significantly higher in response to moving stimuli as compared to stationary stimuli. This confi rms the involvement of the right middle temporal gyrus in the observation of movements. The black-and-white checkerboard stimuli of various shapes, pattern and size, stationary and moving was found to 1) activate visual as well as other cortices in temporal and parietal lobes, 2) cause asymmetry in brain function and 3) exhibit functional integration characteristics in several brain areas.
Keywords: fMRI; SPM; visual stimulus; occipital gyrus; middle temporal gyrus
Heschl’s gyrus (HG) is known to interact with other auditory related areas of the same hemisphere during the performance
of an auditory cognitive task. However, the information about how it interacts with the opposite HG is still lacking.
The aim of this study was to investigate the psychophysiologic interaction (PPI) between the bilateral HG during a
simple arithmetic addition task and to verify the role of noise as an experimental factor that would modulate the PPI.
Functional magnetic resonance imaging (fMRI) scans were performed on eighteen healthy participants, in which a
single-digit addition task were solved during in-quiet (AIQ) and in-noise (AIN) conditions. The fMRI data were analysed
using Statistical Parametric Mapping (SPM8). The interaction between the bilateral HG was investigated using PPI
analysis. The response in right HG was found to be linearly influenced by the activity in left HG, vice-versa, for both
in-quiet and in-noise conditions. The connectivity from right to left HG in noisy condition seemed to be modulated
by noise, while the modulation is relatively small oppositely, indicating a non-reciprocal behavior. A two-way PPI
model between right and left HG is suggested. The connectivity from right to left HG during a simple addition task in
noise is driven by a higher ability of right HG to perceive the stimuli in a noisy condition. Both the bilateral HGs took
part in the cognitive processes of arithmetic addition from which the interactions between the two were found to be
different in noise.
This study was carried out to investigate the effects of noisy background on brain activation during a working memory task. Fourteen healthy male subjects underwent silent functional Magnetic Resonance Imaging (fMRI) scans while listening to words presented verbally against quiet (WIS) and noisy (WIN) backgrounds. The stimuli were binaurally presented to the subjects at 70 dB sound pressure level (SPL) in both conditions. Group results indicated significant (p < 0.001) bilateral widespread of brain activations in the primary auditory cortex, superior temporal gyrus, inferior frontal gyrus, supramarginal gyrus and inferior parietal lobes during WIS. Additional significant activation was observed in the middle cingulate cortex and anterior cingulate cortex during WIN, suggesting the involvement of cingulate cortex in working memory processing against a noisy background. The mean percentage of signal change in all regions was higher during WIN as compared to WIS. Right hemispheric predominance was observed for both conditions in primary auditory cortex and middle frontal gyrus and this could be attributed to the increased difficulty of the tasks. The results obtained from this study demonstrated that background noise increased task demand and difficulty. Task demand was found to play an important role in determining the activation magnitude in the brain areas during working memory task.
In this multiple-subject study, intrinsic couplings between the primary motor (M1) and supplementary motor areas (SMA) were investigated. Unilateral (UNIright and UNIleft) self-paced tapping of hand fingers were performed to activate M1 and SMA. The intrinsic couplings were analysed using statistical parametric mapping, dynamic causal modeling (DCM) and Bayesian model analysis. Brain activation observed for UNIright and UNIleft showed contralateral and ipsilateral involvement of M1 and SMA. Ten full connectivity models were constructed with right and left M1 and SMA as processing centres. DCM indicated that all subjects prefer M1 as the intrinsic input for UNIright and UNIleft as indicated by a large group Bayes factor (GBF). Positive evidence ratio (PER) that showed strong evidence of Model 3 and Model 6 against other models in at least 12 out of 16 subjects, supported GBF results. The GBF and PER results were later found to be consistent with that of BMS for group studies with high expected posterior probability and exceedance probability. It was concluded that during unilateral finger tapping, the contralateral M1 would act as the input centre which in turn triggered the propagation of signals to SMA in the same hemisphere and to M1 and SMA in the opposite hemisphere.