string: The unit recording with silicon probe can be obtained routinely and these results in freely moving rats have been described in many earlier publications (Buzsáki et al., 1992; Bragin et al., 1995, 1996, 1997; Ylinen et al., 1995; Chrobak and Buzsáki, 1996, 1998; Kandel and Buzsáki, 1997).