Table 1.

Summaries on the effects of E2 treatment on cognitive performance of castrated male rats. Data were compared to the Control group, which consists of castrated rats without E2 treatment.

Cognitive Domain Tested (Testing Apparatus)	Studies		Effects of E2 Treatment		Parameters Measured
Spatial learning
Barnes maze	[71]		↑		Changes in path length, latency to find a goal box, and number of errors on Day 1 testing.
Barnes maze	[25]		↑		Changes in path length, latency to find a goal box, and number of errors on Day 1 testing.
Cross-maze	[23]		↑		Percentage of correct choices between the first and fourth day of testing.
Operant conditioning chamber	[15]		0		Number of sessions to reach 25 correct choices in a single session; i.e., to alternately press 2 levers for water reward.
T-maze	[61]		↑		Percentage of trials with a correct response; i.e., to visit an arm in which the rats previously received a food reward.
T-maze	[13]		0		Number of sessions to reach 7 correct choices in 9 tests; i.e., to visit alternating baited (with water reward) arm consecutively.
Radial arm maze	[60]		0		Number of trials to obtain 7 correct choices in the first 8 visits—to get food reward in 8 arms—in 5 consecutive trials.
Spatial working memory
Barnes maze	[71]		↑ on Day 1 0 on Day 2		Spatial working memory error was measured from the number of re-investigation of incorrect holes.
Barnes maze	[25]		↑ on Day 1 0 on Day 2		Spatial working memory error was measured from the number of re-investigation of incorrect holes.
Open field with 2 identical objects	[63]		↑		Time spent exploring moved and unmoved objects.
Morris water maze	[26]		↓ with EB 0 with ED		Changes in escape latency between the final and first day of testing.
T-maze	[61]		0		Percentage of trials with a correct response (to visit an arm in which the rats previously received a food reward) after the maze was rotated and inter-trial delay was increased.
Radial arm maze	[60]		Data not shown		The number of re-entries into previously visited arm was collected (indicative of working memory errors) but data were not shown.
Spatial reference memory
Barnes maze	[71]		0		Path length and latency to find a goal box on Day 2 (1 day delay) testing. Spatial reference memory error was measured from the number of first-time investigation of incorrect holes.
Barnes maze	[25]		0 on Day 2 ↑ on Day 7		Path length and latency to find a goal box on Day 2 (1 day delay) and Day 7 (1 week delay) testing. Spatial reference memory error was measured from the number of first-time investigation of incorrect holes.
Morris water maze	[26]		0		Escape latency (i.e., time to find a submerged platform).
Cross-maze	[23]		↑		Averaged percentage of correct choices in 4 days of testing.
T-maze	[61]		0		Percentage of trials with a correct response; i.e., to visit an arm in which the rats previously received a food reward.
Radial arm maze	[60]		0 with no delay ↑ with delay		Number of correct choices (visits to baited arms) in the first 8 visits. Trials were done with and without 1-hour delay between the 4th and 5th arm visits.
Cognitive Domain Tested (Testing Apparatus)		Studies		Effects of E2 Treatment		Parameters Measured
Object recognition memory
Open field with 2 objects		[21]		0		Time spent exploring novel and old objects.
Learning of extradimensional shift
Operant conditioning chamber		[15]		0		Number of sessions to reach 90% accuracy of a task; i.e., to press a lever with a cue light in order to receive a water reward; another lever with unlit lamp was present simultaneously.
Withholding response
Operant conditioning chamber		[15]		↑		Percentage of impulsive lever press over total lever press.
Motivation for reward
Operant conditioning chamber		[15]		↑		Number of water reward obtained.
Behavioural flexibility (learning of match or non-match-to-position)
Operant conditioning chamber		[15]		0		Number of sessions to reach 90% accuracy of a task; i.e., in a pair of testing phases, rats needed to either press the same (match) or a different (non-match) lever in the second test as that in the first test in order to get a water reward.
Learning of configural association negative patterning
Operant conditioning chamber		[61]		0		Changes in the number of responses (i.e., to enter a food cup for reward) and time to respond following a tone, light or both stimuli.

↑↓ = Significantly better or worse performance than castrated rats with no hormone treatment. 0 = No significant effect. E2 = Estradiol. EB = Estradiol benzoate. ED = Estradiol dipropionate.