Journal of Neuroscience, Vol 1, 1268-1278, Copyright © 1981 by Society for Neuroscience
Visual responses of single neurons in the caudal lateral pulvinar of the macaque monkey
LA Benevento and J Miller
Single unit recordings were made in the portion of the lateral pulvinar
which forms the lateral aspect of the caudal pole of the thalamus, i.e., PL
gamma (Rezak, M., and L. A. Benevento (1977) Soc. Neurosci. Abstr. 3:573;
Rezak, M. (1978) Soc. Neurosci. Abstr. 4: 642), of macaque monkeys. PL
gamma receives convergent inputs from the occipital cortex and has strong
reciprocal interconnections with the visual association cortex, including
the inferotemporal cortex (areas 20 and 21). It was found the that PL gamma
has a poor or nonexistent retinotopic organization. Many of the neurons had
large, unflanked, overlapping receptive fields which often included the
fovea. A few neurons could be influenced by a visual stimulus placed
anywhere in the visual field described by a tangent screen. The receptive
fields could be bilateral or located entirely within the contralateral or
ipsilateral hemifields. The majority of units were binocular and exhibited
various types of binocular interaction which could be quite complex. The
binocular response was not predictable from the algebraic sum of the
monocular responses and could be of the opposite sign (e.g., excitatory
when the monocular response was inhibitory). Neurons which were also
sensitive to the direction of movement of stimuli projected upon the
tangent screen formed a major group. Of the units sensitive to tangentially
moving stimuli, two special subgroups were found. One group of neurons gave
sustained responses to static levels of luminance, while the other group
was sensitive to simuli which moved toward or away from the eyes. The
nonlinear rate of change of the apparent size of approaching or receding
stimuli was described by a mathematical function which also describes the
response of the neurons to the same stimuli. For many of these units which
were sensitive to tangentially moving stimuli and one other class of
stimuli, such as luminance levels of movement in depth, the responses to
one class were seemingly unrelated to the responses to the other class. The
same statement may be made for monocular and binocular responses. It may
be, then, that different wiring diagrams describe these different types of
inputs. These physiological results are discussed in terms of the inputs to
PL gamma as well as its cortical targets.