Fig. 2. (A) Muscle activity (electromyographs) during swimming in a larval lamprey (whole animal). (Ai) Diagram of a larval lamprey with EMG recording electrodes (1-4; see Materials and methods for positions of electrodes). (Aii) Episode of spontaneous locomotor muscle activity, characterized by a left—right alternation (12) and a rostrocaudal phase lag (23 and 34). (B) Locomotor activity in preparations in vitro. (Bi) In vitro brain/spinal cord preparation from a lamprey in which pharmacological agents (5 mmol l^-1 D-glutamate/5 mmol l^-1 D-aspartate) were pressure-ejected through micropipettes (PE_R and PE_L) in brain locomotor areas to initiate spinal locomotor activity (see Materials and methods for list of source articles), which was recorded from the ventral roots using suction electrodes (1-4). (Bii) Episode of brain-initiated in vitro locomotor activity (1-4; integrated with =50 ms) elicited by pressure ejection (PE) in the rostrolateral rhombencephalon and characterized by left—right alternation (12) and a rostrocaudal phase lag (23 and 34). Note that phase lags for in vitro locomotor activity are smaller than those for locomotor muscle activity in whole animals, as previously reported (McClellan, 1994). Time scale, 1 s (A); 5 s (B).