Abstract
Although many details remain unknown, several positive statements can be made about the laminar distribution of primate frontal eye field (FEF) neurons with different physiological properties. Most certainly, pyramidal neurons in the deep layer of FEF that project to the brainstem carry movement and fixation signals but clear evidence also support that at least some deep-layer pyramidal neurons projecting to the superior colliculus carry visual responses. Thus, deep-layer neurons in FEF are functionally heterogeneous. Despite the useful functional distinctions between neuronal responses in vivo, the underlying existence of distinct cell types remain uncertain, mostly due to methodological limitations of extracellular recordings in awake behaving primates. To substantiate the functionally defined cell types encountered in the deep layer of FEF, we measured the biophysical properties of pyramidal neurons recorded intracellularly in brain slices issued from macaque monkey biopsies. Here, we found that biophysical properties recorded in vitro permit us to distinguish two main subtypes of regular-spiking neurons, with, respectively, low-resistance and low excitability vs. high-resistance and strong excitability. These results provide useful constraints for cognitive models of visual attention and saccade production by indicating that at least two distinct populations of deep-layer neurons exist.
Highlights
It is becoming increasingly important to determine the identity of cortical neurons involved in a wide range of brain functions
The visual and visuo-movement neurons select the target of search by increasing their firing rate in response to the presence of the target in their receptive fields (RFs) relative to when a distractor is located in their RFs (e.g., Schall and Hanes, 1993; Thompson et al, 1996)
Pyramidal neurons of the frontal eye field (FEF) deep layer (n = 50) were recorded by whole-cell patch-clamp at 34◦C in parasagittal brain slices from tissue block containing the portions of areas 9 and 46 non-homotopic from adult macaque monkeys (n = 8 animals)
Summary
It is becoming increasingly important to determine the identity of cortical neurons involved in a wide range of brain functions. In the oculomotor field of research, it has been demonstrated that several cortical areas and subcortical regions contribute to the visual-motor mapping. One such area, the frontal eye field (FEF), contains at least three main functional types of neurons: visual, movement, and visuomovement neurons (Goldberg and Bushnell, 1981; Bruce and Goldberg, 1985; Segraves and Goldberg, 1987; Schall, 1991; Segraves, 1992; Kodaka et al, 1997; Umeno and Goldberg, 1997; Hanes et al, 1998; DiCarlo and Maunsell, 2005). Visuo-movement neurons increase their firing rate leading up to saccades while they respond to the presence of the target in RFs (Everling and Munoz, 2000; Sato et al, 2001; McPeek, 2006; Ray et al, 2009)
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