Discharge of frontal eye field neurons during eye movements in unanesthetized monkeys.
ABSTRACT Single unit activity was recorded from the frontal eye fields (area 8) in unanesthetized monkeys seated in a primate chair with the head restrained. The frontal eye field units were identified by antidromic response to stimulation of the cerebral peduncle. The findings indicate that most of the neurons discharge only after initiation of eye movements. These cells showed steady discharge when the eyes were immobile and oriented in a specific direction.
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ABSTRACT: For over a century, electrical microstimulation has been the most direct method for causally linking brain function with behavior. Despite this long history, it is still unclear how the activity of neural populations is affected by stimulation. For example, there is still no consensus on where activated cells lie or on the extent to which neural processes such as passing axons near the electrode are also activated. Past studies of this question have proven difficult because microstimulation interferes with electrophysiological recordings, which in any case provide only coarse information about the location of activated cells. We used two-photon calcium imaging, an optical method, to circumvent these hurdles. We found that microstimulation sparsely activates neurons around the electrode, sometimes as far as millimeters away, even at low currents. Our results indicate that the pattern of activated neurons likely arises from the direct activation of axons in a volume tens of microns in diameter.Neuron 09/2009; 63(4):508-22. · 15.77 Impact Factor
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ABSTRACT: The path from perception to action involves the transfer of information across various reference frames. Here we applied a functional magnetic resonance imaging (fMRI) repetition suppression paradigm to determine the reference frame(s) in which the cortical activity is coded at several phases of the sensorimotor transformation for a saccade, including sensory processing, saccade planning, and saccade execution. We distinguished between retinal (eye-centered) and nonretinal (e.g., head-centered) coding frames in three key regions: the intraparietal sulcus (IPS), frontal eye field (FEF), and supplementary eye field (SEF). Subjects (n = 18) made delayed saccades to one of five possible peripheral targets, separated at intervals of 9° visual angle. Target locations were chosen pseudorandomly, based on a 2 × 2 factorial design, with factors retinal and nonretinal coordinates and levels novel and repeated. In all three regions, analysis of the blood oxygenation level dependent dynamics revealed an attenuation of the fMRI signal in trials repeating the location of the target in retinal coordinates. The amount of retinal suppression varied across the three phases of the trial, with the strongest suppression during saccade planning. The paradigm revealed only weak traces of nonretinal coding in these regions. Further analyses showed an orderly representation of the retinal target location, as expressed by a contralateral bias of activation, in the IPS and FEF, but not in the SEF. These results provide evidence that the sensorimotor processing in these centers reflects saccade generation in eye-centered coordinates, irrespective of their topographic organization.Journal of Neurophysiology 09/2010; 104(3):1239-48. · 3.30 Impact Factor
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ABSTRACT: The frontal eye fields (FEF), originally identified as an oculomotor cortex, have also been implicated in perceptual functions, such as constructing a visual saliency map and shifting visual attention. Further dissecting the area's role in the transformation from visual input to oculomotor command has been difficult because of spatial confounding between stimuli and responses and consequently between intermediate cognitive processes, such as attention shift and saccade preparation. Here we developed two tasks in which the visual stimulus and the saccade response were dissociated in space (the extended memory-guided saccade task), and bottom-up attention shift and saccade target selection were independent (the four-alternative delayed saccade task). Reversible inactivation of the FEF in rhesus monkeys disrupted, as expected, contralateral memory-guided saccades, but visual detection was demonstrated to be intact at the same field. Moreover, saccade behavior was impaired when a bottom-up shift of attention was not a prerequisite for saccade target selection, indicating that the inactivation effect was independent of the previously reported dysfunctions in bottom-up attention control. These findings underscore the motor aspect of the area's functions, especially in situations where saccades are generated by internal cognitive processes, including visual short-term memory and long-term associative memory.PLoS ONE 01/2012; 7(6):e39886. · 3.73 Impact Factor