Table 1.

Statistical moments of the distributions of normalized spike counts associated with single-unit recordings made to novel and repeated items

	Hippocampus		Amygdala		Anterior cingulate		Prefrontal
	Repeated	Novel	Repeated	Novel	Repeated	Novel	Repeated	Novel
Mean	−0.007	−0.015	0.039	0.025	0.032	0.037	−0.023	−0.042
SD	0.99	1.007	1.049	1.022	1.053	1.041	0.978	0.988
Skewness	2.77	2.09	1.97	2.02	2.43	2.53	2.84	2.62
Kurtosis	20.11	6.44	5.75	6.69	11.49	12.84	14.43	11.91

With regard to both skewness and kurtosis, the difference between repeated vs. novel items was significant only in the hippocampus (P = 0.002 and P = 0.006, respectively). With regard to both the mean and the SD, the difference between the repeated vs. novel item spike-count distributions was not significant in any of the four brain regions.

The mean and SD are less sensitive to the presence of outliers than are skewness and kurtosis (25).