Table 1.

The number of neuron pairs, significant excitatory connections, and the experimentally derived detection probability of excitatory connection pairs p_αⁿ in our data counted in three different ways for comparison with intracellular and extracellular recording studies

Datasets	Counting method
	Song et al. (2005)	Present study	Fujisawa et al., (2008)
Rat 1
Novel
No. neuron pairs	36	276	820*
No. EE1 connections	5	6	6
No. EE2 connections	1	1	1
No. unconnected pairs	30	269	813*
pαn (connectivity)**	0.10	0.01	0.00
Sequence
No. neuron pairs	22	210	528*
No. EE1 connections	9	12	12
No. EE2 connections	2	3	3
No. unconnected pairs	11	195	513*
pαn (connectivity)**	0.30	0.04	0.02
Rat 2
Novel
No. neuron pairs	26	153	780*
No. EE1 connections	2	2	2
No. EE2 connections	1	1	1
No. unconnected pairs	23	150	777*
pαn(connectivity)**	0.08	0.01	0.00
Sequence
No. neuron pairs	5	55	325*
No. EE1 connections	1	1	1
No. EE2 connections	0	0	0
No. unconnected pairs	4	54	324*
pαn (connectivity)**	0.10	0.01	0.00
Rat 3
Novel
No. neuron pairs	77	253	903*
No. EE1 connections	4	4	4
No. EE2 connections	0	0	0
No. unconnected pairs	73	249	899*
pαn (connectivity)**	0.03	0.01	0.00
Sequence
No. neuron pairs	109	496	1431*
No. EE1 connections	6	10	10
No. EE2 connections	9	3	3
No. unconnected pairs	100	483	1418*
pαn (connectivity)**	0.11	0.02	0.01
Total No. neuron pairs	275	1443	4787*

*Includes inhibitory and unclassified neurons as well as excitatory neurons, whereas all other counts contain excitatory neurons only;

**α = abs, n = 25.

The number of neuron pairs, the number of unidirectional excitatory connections (EE1), the number of reciprocal excitatory connections (EE2), and the number of unconnected neuron pairs (NO), as well as the connection probability (detection probability of excitatory connections, p_α²⁵, Eq. 1) for the 25 h recordings are reported in three different ways in order to compare them to intracellular recording studies (Song et al., 2005) and to extracellular recordings (Fujisawa et al., 2008 and the counting method in this paper, in which we only consider excitatory neurons across all tetrodes). Therefore, all three columns contain our data, simply reported according to three different counting methods, which are detailed below.

Formula for calculating the number of neuron pairs for Song et al. (2005) criteria:

where n_EE,i is the total number of excitatory neurons within tetrode i and N_TT is the total number of tetrodes.

Formula for calculating the number of neuron pairs for our criteria:

where n_EE is the total number of excitatory neurons.

Formula for calculating the number of neuron pairs for Fujisawa et al. (2008) criteria:

where n_all is the total number of all recorded neurons, including inhibitory and unclassified neurons.

The formula for calculating the connection probability of excitatory neuron pairs p_αⁿ was provided by Equation 1.