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Reversible inactivation of macaque dorsomedial frontal cortex: effects on saccades and fixations
1Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge 02139, USA. mas@lsr.nei.nih.gov
Abstract:
Neural recording and electrical stimulation results suggest that the dorsomedial frontal cortex (DMFC) of macaque is involved in oculomotor behavior. We reversibly inactivated the DMFC using lidocaine and examined how saccadic eye movements and fixations were affected. The inactivation methods and monkeys were the same as those used in a previous study of the frontal eye field (FEF), another frontal oculomotor region. In the first stage of the present study, monkeys performed tasks that required the generation of single saccades and fixations. During 15 DMFC inactivations, we found only mild, infrequent deficits. This contrasts with our prior finding that FEF inactivation causes severe, reliable deficits in performance of these tasks. In the second stage of the study, we investigated whether DMFC inactivation affected behavior when a monkey was required to make more than one saccade and fixation. We used a double-step task: two targets were flashed in rapid succession and the monkey had to make two saccades to foveate the target locations. In each of five experiments, DMFC inactivation caused a moderate, significant deficit. Both ipsi- and contraversive saccades were disrupted. In two experiments, the first saccades were made to the wrong place and had increased latencies. In one experiment, first saccades were unaffected, but second saccades were made to the wrong place and had increased latencies. In the remaining two experiments, specific reasons for the deficit were not detected. Saline infusions into DMFC had no effect. Inactivation of FEF caused a larger double-step deficit than did inactivation of DMFC. The FEF inactivation impaired contraversive first or second saccades of the sequence. In conclusion, our results suggest that the DMFC makes an important contribution to generating sequential saccades and fixations but not single saccades and fixations. Compared with the FEF, the DMFC has a weaker, less directional, more task-dependent oculomotor influence.
Insights
The dorsomedial frontal cortex (DMFC) is crucial for sequential eye movements but not single ones. Inactivating the DMFC caused mild deficits in single saccades but moderate deficits in sequential saccades, unlike the frontal eye field (FEF).
Area of Science:
- Neuroscience
- Oculomotor Systems
- Cognitive Neuroscience
Background:
- The dorsomedial frontal cortex (DMFC) is implicated in oculomotor behavior.
- Previous research suggests the frontal eye field (FEF) plays a significant role in saccadic eye movements.
Purpose of the Study:
- To investigate the role of the DMFC in saccadic eye movements and fixations.
- To compare the effects of DMFC inactivation with FEF inactivation on oculomotor tasks.
Main Methods:
- Reversible inactivation of the DMFC in macaque monkeys using lidocaine.
- Performance assessment on tasks involving single saccades, fixations, and a double-step saccade task.
- Comparison with prior FEF inactivation studies using identical methodologies.
Main Results:
- DMFC inactivation resulted in mild, infrequent deficits in single saccade and fixation tasks.
- DMFC inactivation caused moderate, significant deficits in the double-step task, disrupting sequential saccades.
- FEF inactivation produced more severe deficits in both single and sequential saccade tasks compared to DMFC inactivation.
Conclusions:
- The DMFC is important for generating sequential saccades and fixations, but not single ones.
- The DMFC exerts a weaker, less directional, and more task-dependent oculomotor influence than the FEF.