Non-uniform conduction timeintheolivocerebellar pathway intheanaesthetized cat

1. Ithasrecently beendemonstrated thatconduction velocities ofcerebellar climbing fibre afferents intherataretuned according tofibre length suchthat conduction timebetween their origin intheinferior olive andtheir target cortical Purkinje cells isconstant. Herewe haveexamined thesituation inthecat, whereindividual climbing fibres aresubstantially longer. Complex spike responses ofPurkinje cells located atvarious depths inthevermis (zones aandb)wereevoked byelectrical stimulation ofolivocerebellar fibres close totheir origin andwererecorded either extra- orintracellularly. 2. Theonsetlatencies ofdirectly evoked complex spikes ranged from2-6to6-9ms.A consistent trend ineachelectrode penetration wasthatthecomplex spike latencies were longer forthesuperficially encountered cells (where olivocerebellar fibre length isgreatest) andshorter fordeeper cells (where olivocerebellar fibre length isshorter). 3. Linear regression analysis suggests that conduction timeinolivocerebellar fibres inthecatis notfixed butvaries linearly withconduction distance. Ourfindings wouldbeconsistent withauniform conduction velocity inolivocerebellar fibres ofabout 6-6m s-'.