Reversible inactivation of macaque dorsomedial frontal cortex: effects on saccades and fixations |
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| Authors: | Marc A Sommer Edward J Tehovnik |
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| Institution: | (1) Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA, US;(2) Laboratory of Sensorimotor Research, N.E.I., National Institutes of Health, Building 49, Room 2A50, 9000 Rockville Pike, Bethesda, MD 20892–4435, USA e-mail: mas@lsr.nei.nih.gov Tel.: +1-301-496-1141, Fax: +1-301-402-0511, US |
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| 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.
Received: 12 January 1998 / Accepted: 17 July 1998 |
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| Keywords: | Saccadic eye movements Fixations Dorsomedial frontal cortex Supplementary eye field Frontal eye field Reversible inactivation |
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