Prefrontal neuronal activity encodes spatial target representations sequentially updated after nonspatial target-shift cues.
We examined prefrontal neuronal activity while monkeys performed a sequential target-shift task, in which, after a positional cue indicated the initial saccade target among 8 peripheral positions, the monkeys were required to internally shift the target by one position on every flash of a target-shift cue. The target-shift cue appeared in the center 0 to 3 times within a single trial and was always the same in shape, size, and color. We found selective neuronal activity related to the target position: when the target-shift cue implied the target shift to particular peripheral positions, neurons exhibited early-dominant and late-dominant activity during the following delay period. The early-dominant target-selective activity emerged early in the delay just after the presentation of the target-shift cue, whereas the late-dominant activity gradually built up toward the end of the delay. Because the target-shift cue was not related to any specific target location, the early-dominant target-selective activity could not be a mere visual response to the target-shift cue. We suggest that the early-dominant activity reflects the transitory representation for the saccade target that was triggered by the nonspatial target-shift cue, whereas the late-dominant activity reflects the target representation in the spatial working memory or the preparatory set for the possible impending saccade, being repeatedly updated during sequential target shifts.
Department of Physiology, The University of Tokyo School of Medicine, Tokyo 113-0033, Japan.
Tetsuya
T
Fukushima
Isao
I
Hasegawa
Yasushi
Y
Miyashita
D000818:Animals; D003463:Cues; D016208:Databases, Factual; D004567:Electrodes, Implanted; D007839:Functional Laterality / Q000502:physiology; D008251:Macaca; D008570:Memory, Short-Term / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D011153:Population; D017397:Prefrontal Cortex / Q000166:cytology / Q000502:physiology*; D011597:Psychomotor Performance; D012044:Regression Analysis; D012438:Saccades / Q000502:physiology; D013028:Space Perception / Q000502:physiology*