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Identifier 000410080
Title Involvement of the premotor cortex in saccade and forelimb movement generation
Alternative Title Νευροφυσιολογική διερεύνηση της συμμετοχής του προκινητικού φλοιού στις κινήσεις οφθαλμού και άνω άκρου
Author Νερομυλιώτης, Ελευθέριος
Thesis advisor Μοσχοβάκης, Αντώνης
Abstract To study the response properties of cells that could participate in eye-hand coordination, we performed extracellular recordings from two macaque monkeys performing center-out saccades and forelimb pointing movements. We analyzed the phasic movement related discharges of neurons in the periarcuate cortex and separated them in seven distinct classes, based on the presence or absence of such phasic discharge before saccades, hand movements or combined eye-hand movements. We encountered 55 cells that fired before and during saccades and movements of the hand. Because they could encode an abstract form of the desired displacement vector without regard to the effector that would execute the movement, we refer to this class of cells as motor equivalence neurons (Meq). The onset of the phasic discharges of Meq cells was often correlated to both the onset of saccades and the onset of hand movements. Their on-directions were uniformly distributed without preference for ipsiversive or contraversive movements. In about half of the cells the preferred direction for saccades was the preferred direction for hand movements as well. In the remaining cells the difference was considerable (>90 deg). A three-layer neural network model that used Meq cells as its input layer showed that the lack of effector invariance in their discharge can help reduce the number of decoding errors when the network attempts to compute the correct movement metrics of the right effector. We also found in the caudal bank of the arcuate sulcus cells that discharged in relation to saccades and not hand movements (S neurons). Unlike frontal eye field (FEF) presaccadic neurons, the on-directions of premotor S neurons had equal probability to be ipsiversive or contraversive. Since the onset of the phasic discharge S cells preceded that of FEF presaccadic neurons, they are unlikely to convey to their targets corollary discharges of signals arising in area 8. Apart from the familiar premotor cells discharging before forelimb movements (H cells), we encountered a small number of neurons that could function as logical gates: cells that discharged for saccades if they were not accompanied by hand movements (xS neurons), cells that discharged for hand movements if they were not accompanied by saccades (xH neurons), cells that discharged only for coordinated movements of the eyes and the hand (AND neurons) SUMMARY viii and cells that discharged for saccades or movements of the hand but did not discharge for coordinated movements of both effectors (XOR neurons). Our findings are discussed in the context of sequences of decision processes stitching effector specific motor plans onto effector invariant movement primitives. Finally, to test the hypothesis that the premotor cortex in and behind the caudal bank of the arcuate sulcus can generate saccades, we stimulated electrically the periarcuate frontal cortex of alert rhesus monkeys. We were able to produce saccades from sites of the premotor cortex that were contiguous with the frontal eye fields and extended up to 2mm behind the smooth pursuit area. Premotor sites elicited saccades with ipsiversive characteristic vectors. Premotor generated saccades had also lower peak velocities and flatter velocity profiles than FEF generated saccades.
Language English
Issue date 2017-07-26
Collection   School/Department--School of Medicine--Department of Medicine--Doctoral theses
  Type of Work--Doctoral theses
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