Classical eye-blink conditioning in mutant mice can be used to study the
molecular mechanisms underlying associative learning. To measure the
kinetic and frequency domain properties of conditioned (tone - periorbital
shock procedure) and unconditioned eyelid responses in freely moving mice,
we developed a method that allows adequate, absolute, and continuous
determination of their eyelid movements in time and space while using an
electrical shock as the unconditioned stimulus. The basic principle is to
generate a local magnetic field that moves with the animal and that is
picked up by either a field-sensitive chip or coil. With the use of this
magnetic distance measurement technique (MDMT), but not with the use of
electromyographic recordings, we were able to measure mean latency, peak
amplitude, velocity, and acceleration of unconditioned eyelid responses,
which equaled 7.9 +/- 0.2 ms, 1.2 +/- 0.02 mm, 28.5 +/- 1 mm/s, and 637
+/- 22 mm/s(2), respectively (means +/- SD). During conditioning, the mice
reached an average of 78% of conditioned responses over four training
sessions, while animals that were subjected to randomly paired conditioned
and unconditioned stimuli showed no significant increases. The mean
latency of the conditioned responses decreased from 222 +/- 40 ms in
session 2 to 127 +/- 6 ms in session 4, while their mean peak latency
increased from 321 +/- 45 to 416 +/- 67 ms. The mean peak amplitudes, peak
velocities, and peak acceleration of these responses increased from 0.62
+/- 0.02 to 0.77 +/- 0.02 mm, from 3.9 +/- 0.3 to 7.7 +/- 0.5 mm/s, and
from 81 +/- 7 to 139 +/- 10 mm/s(2), respectively. Power spectra of
acceleration records illustrated that both the unconditioned and
conditioned responses of mice had oscillatory properties with a dominant
peak frequency close to 25 Hz that was not dependent on training session,
interstimulus interval, or response size. These data show that MDMT can be
used to measure the kinetics and frequency domain properties of
conditioned eyelid responses in mice and that these properties follow the
dynamic characteristics of other mammals