Are primate lateral geniculate nucleus (LGN) cells really sensitive to orientation or direction?
There is considerable controversy over the existence of orientation and direction sensitivity in lateral geniculate nucleus (LGN) neurons. Claims for the existence of these properties often were based upon data from cells tested well beyond their peak spatial frequencies. The goals of the present study were to examine the degree of orientation and direction sensitivity of LGN cells when tested at their peak spatial and temporal frequencies and to compare the tuning properties of these subcortical neurons with those of visual cortex. For this investigation, we used conventional extracellular recording to study orientation and direction sensitivities of owl monkey LGN cells by stimulating cells with drifting sinusoidal gratings at peak temporal frequencies, peak or higher spatial frequencies, and moderate contrast. A total of 110 LGN cells (32 koniocellular cells, 34 magnocellular cells, and 44 parvocellular cells) with eccentricities ranging from 2.6 deg to 27.5 deg were examined. Using
