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Kathy T. Mullen, Benjamin Thompson, Robert F. Hess; Response of the human LGN to different temporal frequencies for achromatic, L/M opponent and S-cone opponent stimuli measured with high field fMRI. Journal of Vision 2008;8(6):808. doi: https://doi.org/10.1167/8.6.808.
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© ARVO (1962-2015); The Authors (2016-present)
Aims. We compare the responsiveness of the human LGN to different temporal frequencies (2–16Hz) for stimulation of each of the two cone opponent systems (L/M and S-cone) and the achromatic system. For comparison, measurements were also obtained from cortical area V1. Methods. MR images were acquired on a 4T Bruker MedSpec scanner. Stimuli were sinewave counter-phasing rings (0.5cpd, 2, 4, 8 Hz for chromatic stimuli and 2, 8 & 16 Hz for achromatic stimuli) that selectively activated the L/M cone opponent (RG), S cone opponent (BY) or achromatic (Ach) systems. Stimuli were presented in a temporal Gaussian envelope (s=125ms) at high cone contrasts (11% Ach; 4% RG; 30% BY). The LGNs of 6 subjects were localized in separate scans using broadband stimuli. V1s were mapped previously (Mullen et al., Euro. J. Neuroscience, 2007). We performed region of interest analyses on all LGNs and V1s and results are based on average time courses. Results. for achromatic stimuli, the human LGN shows a declining response with increasing TF (2–16Hz), which also occurs but is less marked in V1. For RG stimuli, the LGN shows some loss of response across TF from 2 to 8Hz, whereas the V1 response is unaffected by TF. For BY stimuli, the response shows some peaking at 4Hz in the LGN, but has no dependence on TF in V1 (2–8Hz). Conclusions. We find that for our stimuli the BOLD response of the LGN is optimal at low temporal frequencies (2–4Hz) for both achromatic and chromatic stimuli. This contrasts with previous results for achromatic stimuli which show a rise in response with increasing temporal frequency (Kastner et al., J. Neurophysiol., 2004).
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