Functional Magnetic Resonance Imaging (fMRI) on Saccade vs Pursuit at 3T

Purpose: To identify the anatomical correlates of saccadic and pursuit voluntary predictive eye movements based on fMRI at 3T. Methods: fMRI was undertaken utilizing a 3.0T GE system scanning the whole head and the BOLD technique. Data analysis was carried out using FEAT (FMRI Expert Analysis Tool) Version 5.4 (FMRIB’s Software Library, www.fmrib.ox.ac.uk/fsl). Saccadic and pursuit eye movements were elicited using a white dot (0.5 cm in diameter and average visual dot size of 0.66º ) moving horizontally (19º from center in each direction) at 0.5Hz with binocular viewing. Subjects included 7 normal adults ranging in age from 18-54 years with normal visual acuity (20/20 or better) and normal stereoacuity (40 sec of arc or better). Results: Average activation across the seven subjects with p\u3c0.05 showed more activation sites with saccadic eye movements (X² = 12.37, p\u3c.001). The culmen in the cerebellum was activated with both saccades and pursuit; however not in the same location. Activation was found in the tuber and uvula of the cerebellum only with saccades. Brodmann areas 4,6,7,9,18,19,21,32,37,38, and 46 were activated with saccades while Brodmann areas 7,8,36,37 were activated in pursuit. Conclusions: When whole brain imaging is employed with 3T fMRI, a significantly greater number of activated areas are found with saccadic as opposed to pursuit eye movements, with a number of overlapping sites responsible for both types of eye movements

Functional Magnetic Resonance Imaging (fMRI) on Saccade vs Pursuit at 3T

Purpose: To identify the anatomical correlates of saccadic and pursuit voluntary predictive eye movements based on fMRI at 3T. Methods: fMRI was undertaken utilizing a 3.0T GE system scanning the whole head and the BOLD technique. Data analysis was carried out using FEAT (FMRI Expert Analysis Tool) Version 5.4 (FMRIB’s Software Library, www.fmrib.ox.ac.uk/fsl). Saccadic and pursuit eye movements were elicited using a white dot (0.5 cm in diameter and average visual dot size of 0.66º ) moving horizontally (19º from center in each direction) at 0.5Hz with binocular viewing. Subjects included 7 normal adults ranging in age from 18-54 years with normal visual acuity (20/20 or better) and normal stereoacuity (40 sec of arc or better). Results: Average activation across the seven subjects with p\u3c0.05 showed more activation sites with saccadic eye movements (X² = 12.37, p\u3c.001). The culmen in the cerebellum was activated with both saccades and pursuit; however not in the same location. Activation was found in the tuber and uvula of the cerebellum only with saccades. Brodmann areas 4,6,7,9,18,19,21,32,37,38, and 46 were activated with saccades while Brodmann areas 7,8,36,37 were activated in pursuit. Conclusions: When whole brain imaging is employed with 3T fMRI, a significantly greater number of activated areas are found with saccadic as opposed to pursuit eye movements, with a number of overlapping sites responsible for both types of eye movements

Instruction Dependent Activation during Optokinetic Nystagmus (OKN) Stimulation: An FMRI Study at 3 T

Modifying experimental conditions of optokinetic nystagmus (OKN) result in different outcomes and may not optimally translate into clinical testing. The purpose of this study was to assess the influence of subject instruction on the anatomical correlates of OKN. The instructions were to voluntarily look or stare at the same moving grating with fixed contrast and spatial and temporal frequencies. Look and stare OKN were generated under identical stimulus “ON” conditions (vertical sine wave grating of 1.14 c/deg drifting right to left at 11.4 c/s with binocular viewing). FMRI was undertaken utilizing a 3.0 T GE system and the BOLD technique. Subjects included 6 normal adults ranging in age from 18 to 54 years with normal visual acuity (20/20 or better) and normal stereoacuity (40 s of arc or better). The results reveal that look OKN generated significantly more cortical FMRI activation than stare OKN. Look OKN areas included the culmen, parahippocampal, lingual, middle temporal gyri, inferior and superior parietal lobules and precuneus, all of which were unilaterally activated in the left hemisphere. The middle occipital gyrus was unilaterally activated in the right hemisphere while the cuneus was bilaterally activated. These results show that the activation sites for OKN studies are dependent on subject instruction which influence the type of OKN generated. Specifically, voluntary look OKN involved more brain sites than stare OKN. In so doing, we illustrate the importance of subject instruction and recommend that FMRI investigators of OKN be cognizant of these effects. The anatomical correlates of the look versus stare are discussed

Relationship among fMRI, Contract Sensitivity and Visual Acuity

The purpose of this study was to ascertain whether visual acuity or contrast sensitivity function (CSF) is proportional to visual cortical function based on fMRI volume and level of activation or Z-score. Forced choice procedures were utilized to measure the monocular log minimal angle of resolution (logMAR) visual acuity and CSF. The CSF data were collapsed into a single index by the use of weighted mean contrast sensitivity (WMCS), being defined as the mean of the products of each spatial frequency multiplied by its corresponding contrast sensitivity. fMRI data had been obtained with a 1.5 T GE Signa scanner with visual stimuli including 1.0 and 2.0 c/deg vertical sinusoidal gratings. Subjects consisted of eight normal adults and five amblyopic patients, with the amblyopic subjects added to gauge whether the outcome was due to a restricted range of scores or the small number of study participants. In normal subjects, the fMRI volume and level of activation exhibited no statistically significant correlation with visual acuity at P \u3c 0.05. Statistically significant correlations were obtained between WMCS and fMRI volume (R = 0.765, P = 0.027) and fMRI level of activation (R = 0.645, P = 0.007), with right eye stimulation using the 1.0 c/deg grating. On the whole, statistically significant correlations between WMCS and fMRI parameters were maintained when subject age was held constant and when data from the five amblyopic subjects were included to expand the range of values and increase the number of data sets for analysis. fMRI volume and Z-score were more closely associated with the CSF, as defined by WMCS, than visual acuity. The results suggest that the CSF reflects the underlying visual cortical cells responsible for fMRI volume and the level of activation

Instruction Dependent Activation during Optokinetic Nystagmus (OKN) Stimulation: An FMRI Study at 3 T

Modifying experimental conditions of optokinetic nystagmus (OKN) result in different outcomes and may not optimally translate into clinical testing. The purpose of this study was to assess the influence of subject instruction on the anatomical correlates of OKN. The instructions were to voluntarily look or stare at the same moving grating with fixed contrast and spatial and temporal frequencies. Look and stare OKN were generated under identical stimulus “ON” conditions (vertical sine wave grating of 1.14 c/deg drifting right to left at 11.4 c/s with binocular viewing). FMRI was undertaken utilizing a 3.0 T GE system and the BOLD technique. Subjects included 6 normal adults ranging in age from 18 to 54 years with normal visual acuity (20/20 or better) and normal stereoacuity (40 s of arc or better). The results reveal that look OKN generated significantly more cortical FMRI activation than stare OKN. Look OKN areas included the culmen, parahippocampal, lingual, middle temporal gyri, inferior and superior parietal lobules and precuneus, all of which were unilaterally activated in the left hemisphere. The middle occipital gyrus was unilaterally activated in the right hemisphere while the cuneus was bilaterally activated. These results show that the activation sites for OKN studies are dependent on subject instruction which influence the type of OKN generated. Specifically, voluntary look OKN involved more brain sites than stare OKN. In so doing, we illustrate the importance of subject instruction and recommend that FMRI investigators of OKN be cognizant of these effects. The anatomical correlates of the look versus stare are discussed

Relationship among fMRI, Contract Sensitivity and Visual Acuity

The purpose of this study was to ascertain whether visual acuity or contrast sensitivity function (CSF) is proportional to visual cortical function based on fMRI volume and level of activation or Z-score. Forced choice procedures were utilized to measure the monocular log minimal angle of resolution (logMAR) visual acuity and CSF. The CSF data were collapsed into a single index by the use of weighted mean contrast sensitivity (WMCS), being defined as the mean of the products of each spatial frequency multiplied by its corresponding contrast sensitivity. fMRI data had been obtained with a 1.5 T GE Signa scanner with visual stimuli including 1.0 and 2.0 c/deg vertical sinusoidal gratings. Subjects consisted of eight normal adults and five amblyopic patients, with the amblyopic subjects added to gauge whether the outcome was due to a restricted range of scores or the small number of study participants. In normal subjects, the fMRI volume and level of activation exhibited no statistically significant correlation with visual acuity at P \u3c 0.05. Statistically significant correlations were obtained between WMCS and fMRI volume (R = 0.765, P = 0.027) and fMRI level of activation (R = 0.645, P = 0.007), with right eye stimulation using the 1.0 c/deg grating. On the whole, statistically significant correlations between WMCS and fMRI parameters were maintained when subject age was held constant and when data from the five amblyopic subjects were included to expand the range of values and increase the number of data sets for analysis. fMRI volume and Z-score were more closely associated with the CSF, as defined by WMCS, than visual acuity. The results suggest that the CSF reflects the underlying visual cortical cells responsible for fMRI volume and the level of activation

Neural Circuit Involved in Idiopathic Infantile Nystagmus Syndrome Based on fMRI

Purpose: To identify the neural circuitry of idiopathic infantile nystagmus syndrome (INS), characterized by an early onset alternating series of slow and rapid eye movements that can manifest in different waveforms and genetic lines. The neural circuitry of INS is currently unknown. Methods: A novel functional magnetic resonance imaging (fMRI) method, referred to as the null zone fMRI technique, was used to identify the neural circuitry for INS. In the null zone fMRI technique, a gaze position with minimal nystagmus within the null zone was linked to the fMRI off condition and a gaze position with robust nystagmus outside of the null zone was linked to the fMRI on condition. Eye movements were monitored with an fMRI compatible eye tracker and observed in real time to ensure subject compliance in on and off states. Subjects with INS (n = 4) included three family members (a mother and two daughters) with presumed autosomal dominant INS, as well as age- and gender-matched normal controls (n = 3). Results: Three of four subjects with INS demonstrated significant increased activation of the declive of the cerebellum, whereas no normal subjects under identical conditions showed activation of the declive of the cerebellum. Both groups showed significant activation in the occipital lobe (Brodmann areas 17, 18, 19, and cuneus). Conclusion: A novel fMRI method demonstrated that the declive of the cerebellum is actively involved in INS. These are the first results to identify the cerebellum, and specifically the declive, as a possible site involved in the ocular motor dysfunction known as INS

Neural Circuit Involved in Idiopathic Infantile Nystagmus Syndrome Based on fMRI

Purpose: To identify the neural circuitry of idiopathic infantile nystagmus syndrome (INS), characterized by an early onset alternating series of slow and rapid eye movements that can manifest in different waveforms and genetic lines. The neural circuitry of INS is currently unknown. Methods: A novel functional magnetic resonance imaging (fMRI) method, referred to as the null zone fMRI technique, was used to identify the neural circuitry for INS. In the null zone fMRI technique, a gaze position with minimal nystagmus within the null zone was linked to the fMRI off condition and a gaze position with robust nystagmus outside of the null zone was linked to the fMRI on condition. Eye movements were monitored with an fMRI compatible eye tracker and observed in real time to ensure subject compliance in on and off states. Subjects with INS (n = 4) included three family members (a mother and two daughters) with presumed autosomal dominant INS, as well as age- and gender-matched normal controls (n = 3). Results: Three of four subjects with INS demonstrated significant increased activation of the declive of the cerebellum, whereas no normal subjects under identical conditions showed activation of the declive of the cerebellum. Both groups showed significant activation in the occipital lobe (Brodmann areas 17, 18, 19, and cuneus). Conclusion: A novel fMRI method demonstrated that the declive of the cerebellum is actively involved in INS. These are the first results to identify the cerebellum, and specifically the declive, as a possible site involved in the ocular motor dysfunction known as INS