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A matching algorithm was used to select equally sized populations of place

cells from stress and control conditions that had nearly identical firing properties

during session 1. Place cells from control (n = 54) and stress (n = 46) conditions

were assembled into two separate lists and sorted in ascending order of their

spatial information values (bits per second). An index variable for parsing the lists was set

to i = 1, and the following steps were performed. Step 1: If the values at position i

in each list differed by 0.75 bits per second or less, then both of the cells at position i were

kept in the data set (for the time being); i was incremented by 1 and step 1 was

repeated for the next pair of cells. If the values at position i differed by more than

0.75 bits per second, then step 2 was invoked. Step 2: The list containing the smallest

information value at position i was designated as the "deletion list" for this

iteration of the algorithm. If deleting the cell at i-1 (and shifting the remaining cells

upward) caused the new cell pair at i-1 to differ from each other by more than

0.75 bits per second, then the value at i was deleted, the values below were shifted upward

to fill the gap, and step 1 was repeated without incrementing i. If deleting the cell

at i-1 (and shifting the remaining cells upward) did not cause the new cell pair at

list were checked until a cell was found at position i-b that could not be deleted

without causing the new cell pair at i-b of the two lists to differ by more than 0.75

bits per second. One of the cells between positions i-b+1 and i was then chosen for

deletion; the chosen cell was the one that, when deleted, would result in the

smallest difference in mean place field sizes between the two lists. After deleting

this cell, the cells below were shifted upward and step 1 was repeated without

incrementing i. Step 3: The matching procedure was terminated when both lists

contained equal numbers of cells and no pair of cells in the same list position had

spatial information values that differed by more than 0.75 bits per second.