Abstract
The ventral part of lateral prefrontal cortex (VLPF) of the monkey receives strong visual input, mainly from inferotemporal cortex. It has been shown that VLPF neurons can show visual responses during paradigms requiring to associate arbitrary visual cues to behavioral reactions. Further studies showed that there are also VLPF neurons responding to the presentation of specific visual stimuli, such as objects and faces. However, it is largely unknown whether VLPF neurons respond and differentiate between stimuli belonging to different categories, also in absence of a specific requirement to actively categorize or to exploit these stimuli for choosing a given behavior. The first aim of the present study is to evaluate and map the responses of neurons of a large sector of VLPF to a wide set of visual stimuli when monkeys simply observe them. Recent studies showed that visual responses to objects are also present in VLPF neurons coding action execution, when they are the target of the action. Thus, the second aim of the present study is to compare the visual responses of VLPF neurons when the same objects are simply observed or when they become the target of a grasping action. Our results indicate that: (1) part of VLPF visually responsive neurons respond specifically to one stimulus or to a small set of stimuli, but there is no indication of a “passive” categorical coding; (2) VLPF neuronal visual responses to objects are often modulated by the task conditions in which the object is observed, with the strongest response when the object is target of an action. These data indicate that VLPF performs an early passive description of several types of visual stimuli, that can then be used for organizing and planning behavior. This could explain the modulation of visual response both in associative learning and in natural behavior.
Highlights
The ventral part of lateral prefrontal cortex (VLPF) of the monkey receives strong visual input, mainly from inferotemporal cortex
Previous studies on visual responses in LPF mainly focused on the manipulation of visual input for guiding behavior, with paradigms requiring monkeys to learn an arbitrary association between a specific visual stimulus and, for example, a saccade or a reaching m ovement5,31–33, see[3,8,34]
This study had two main aims: the first was to describe and map the responses of VLPF neurons to the observation of a set of visual stimuli, with the only requirement for the monkey to fixate the image, the second was to assess whether prefrontal neurons respond differently to real objects or to their pictures and activate differently when these objects are passively observed or are target of an action
Summary
The ventral part of lateral prefrontal cortex (VLPF) of the monkey receives strong visual input, mainly from inferotemporal cortex. Previous studies on visual responses in LPF mainly focused on the manipulation of visual input for guiding behavior, with paradigms requiring monkeys to learn an arbitrary association between a specific visual stimulus and, for example, a saccade or a reaching m ovement5,31–33, see[3,8,34] Another series of studies assessed the role of prefrontal neurons in the categorization of visual stimuli, for example requiring the monkey to actively discriminate between objects belonging to different c ategories[1,7,35]. In order to assess whether prefrontal neurons categorize visual stimuli even in the absence of a specific instruction we chose stimuli belonging to four semantic macro-categories
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