Fig. 1. Swimming in larval lamprey. (A) Idealized diagram illustrating the
sequential movements, from left to right, of a lamprey swimming in a forward
direction. (B, top) Diagram of a larval lamprey showing the positions of
muscle recording electrodes (1-5). (B, bottom) Idealized locomotor activity
generated during swimming, characterized by left-right alternation (1
2
and 35) and a rostrocaudal phase lag (1
5, 23 and 34).
Parameters of locomotor activity: (i) Cycle time (T), defined as the
time interval between successive cycles or bursts, is inversely related to
burst frequency f(f=1/T) and swimming speed. (ii)
Burst duration (BD) is defined as the interval between the onsets and offsets
of bursts. (iii) Burst proportion (BP) is calculated as the ratio of burst
duration and cycle time (BD/T). (iv) Burst delay (d) is the
interval between rostral and caudal bursts in the same cycle on the same side
of the body. (v) Intersegmental phase lag (
) is calculated as the ratio
of burst delay and cycle time divided by (i.e. normalized to) the number of
intervening body segments (N) between the recording sites
[(d/T)/N].