Abstract
The common marmoset monkey (Callithrix jacchus) is a small new world primate with excellent spatial vision. Previous electrophysiological studies have mapped the gross retinotopy of V1 and some of its response properties (for example Bourne et al, Cereb Cortex 2002 12:1132–45; Fritsches & Rosa, J Comp Neurol 1996, 372:264–82). In this study we present the first optical maps of the fine retinotopic organisation of V1 along with maps of orientation preference from the same regions of cortex.
Specifically, marmosets were anaesthetised and paralysed using standard procedures (McLoughlin & Blasdel, NeuroImage 1998, 7:326–336) and refracted so that they focused onto a computer monitor that contained our moving stimuli. Preference for orientation was mapped by collecting camera frames when the marmoset viewed moving bars of one orientation and subtracting these frames from camera frames collected during presentation of the orthogonal orientation. Images were then processed using a combination of first frame analysis and the extended spatial decorrelation algorithm (Schiessl et al., IEEE Trans. on Biomed. Engin., 2000, 47:573–577.). Retinotopic strips of space were imaged in a similar manner.
Our results demonstrate that V1 exhibits a smooth and regular retinotopic organisation with relatively isotropic cortical magnification, similar to that of the squirrel monkey (Blasdel & Campbell, J Neurosci. 2001, 8286–301). Vertical bands of space run parallel to the V1/V2 border (as determined histologically) with horizontal bands of space running at approximately right angles to the border. Strips of space aligned at 45 and 135 degrees run at intermediate angles. Orientation is mapped continuously over the surface of V1 but we find no obvious correlation between the retinotopic organisation of space and the organisation of orientation preference. This is in agreement with previous results of ours from V1 in the macaque monkey (McLoughlin & Blasdel, 1988, Soc. Neurosci. Abstr. 24:9).