Attentional fixation neurons in frontal agranular cortex: area 6 aB

Mountcastle and his colleagues described the influence of attentive fixation and the angle of fixation upon the excitability of the light-sensitivity neurons in posterior cortex of rhesus monkey (area 7).We found cells in an area of agranular frontal cortex that code attentional processes, although they lacked receptive fields. Preliminary experiments were carried out on one monkey (Macaca nemestrina) trained to press a bar for fixation and saccade tasks. We recorded from 64 cells in a restricted zone of area 6aB, 12 of which responded only when the animal fixated central target actively during fixation or saccade task. None had receptive fields. This discharge might be the expression of motor fields or propioception or an efferent copy signal. Alternatively it may be an expression of attention. To decide between these two alternatives we studied the fixation between trials and during spontaneous behaviour. In relaxed conditions the discharge of the cells was very poor or completely absent when the animal was fixating centrally. These observations suggest that activity of these cells is independent of pure motor processes (motor field, propioception, efferent copy). Therefore, these neural discharges of cells lacking a visual field, may be considered to be an expression of attention, spatially coded in primary position.