Table 2.

Minimal latencies of synaptic actions evoked from the ipsilateral and contralateral PT and from the ipsilateral MLF

1 Latency (in ms) of:	2 i PT	3 co PT	4 i MLF	5 i PT-MLF	6 co PT-MLF
A	Extracellular spikes	5.52 ± 0.18	n.s.	5.74 ± 0.17	**	3.63 ± 0.13	1.81 ± 0.10	*	2.16 ± 0.22
		n = 10	n = 8	n = 18
B	Field potentials	4.76 ± 0.07	*	5.00 ± 0.08	**	3.21 ± 0.15	1.49 ± 0.07	*	1.74 ± 0.09
		n = 18	n = 16	n = 36
C	Monosynaptic EPSPs from MLF	(n = 20)
	EPSPs	4.48 ± 0.06	n.s.	4.74 ± 0.12	**	3.17 ± 0.05	1.38 ± 0.05	n.s.	1.97 ± 0.36
n = 11	n = 11	n = 20
	IPSPs	5.65 ± 0.17	n.s.	5.52 ± 0.10	**	4.02 ± 0.13	1.97 ± 0.36	n.s.	1.67 ± 0.13
n = 11	n = 10	n = 16
	EPSPs–field potentials	−0.17	−0.06	−0.10	—	—
	IPSPs–EPSPs	1.17 ± 0.17	n.s.	0.94 ± 0.17	n.s.	0.91 ± 0.12	—	—
D	Disynaptic EPSPs or no EPSPs from MLF	(n = 9)
	EPSPs	5.95 ± 0.43	n.s.	5.96 ± 0.31	**	4.18 ± 0.11	1.77 ± 0.46	n.s.	1.79 ± 0.33
		n = 4	n = 6	n = 8
	IPSPs	5.97 ± 0.31	n.s.	5.29 ± 0.24*	*	4.53 ± 0.30	1.73 ± 0.13	n.s.	0.93 ± 0.58
		n = 4	n = 5	n = 7
	EPSPs–field potentials	1.30	1.16	0.97	—	—
	IPSPs–EPSPs	−0.04 ± 0.52	n.s.	−0.22 ± 0.44	n.s.	0.17 ± 0.26	—	—

All the data are for stimulus intensities of 100–150 μA. i, ipsilateral; co, contralateral; MLF, medial longitudinal fascicle. Data in A are for extracellularly recorded spike potentials of 18 commissural interneurones antidromically activated from the contralateral GS motor nucleus; in B for field potentials recorded at 36 locations; in C for PSPs recorded in 20 commissural interneurones with monosynaptic EPSPs from the MLF; in D for PSPs recorded in 9 commissural interneurones in which MLF stimuli evoked only disynaptic EPSPs (n= 8) or IPSPs, or had no effect (n= 1). The data show effects evoked by the third or fourth PT stimuli and by the first or second MLF stimuli. Means and s.e.m. of minimal latencies are for events with latencies of less than 7 ms, measured from averages of 10–20 individual records. The numbers of measurements on which these means are based are shown. However, these numbers do not reflect the number of neurones in which PT stimuli evoked spikes, EPSPs or IPSPs because the neurones sometimes deteriorated before effects of different intensities or numbers of stimuli applied to the PTs on both sides and the MLF could be tested. The proportions of neurones in which stimuli with various parameters were effective are given in Table 1. Since the time resolution in the averaged records was 30 μs per address, any differences of the order of ±0.03 ms are considered as being within measurement errors. Statistically significant differences between data in columns 2 and 3, 3 and 4 and 5 and 6 are indicated between the pairs of columns (**P < 0.001; *P < 0.05; n.s., not statistically significant). In addition to those indicated, there was a statistically significant difference between latencies of EPSPs (at P < 0.001) but not of IPSPs of PT origin in C and D.