Does it matter which direction I insert the electrode wire and the pins on an EIB? 

There is no problem with inserting the wire and pins from either direction. However, if a problem occurs with the wire connection, the pin has a better chance of holding the wire more securely, thus maintaining signal connection using the method instructed, which is inserting the wire from the top and pins from the bottom. This is obviously a user preference option and will not affect your recording data. 

Caution – Device for investigational use in laboratory animals or other tests that do not involve human subjects.