A Tactile-visual Conditional Discrimination Task for Testing Spatial Working Memory in Rats

Materials and Reagents

1. Male Long Evans Hooded (Harlan, Indianapolis) rats, weighing between 250 g and 500 g upon arrival (approximately 90 days of age)
   
2. Chocolate Sprinkles are used for food reward. Our lab uses the Chef’s Quality brand
   
3. 70% ethanol for cleaning the maze between daily training sessions
   

Equipment

1. Wooden T-Maze that consists of a central stem (117 x 10 x 5 cm), two goal arms (56.5 x 10 x 5 cm) and two return arms (112 x 10 x 5 cm). The floor of the maze is covered with Roppe black vinyl (3 mm thick) (Figure 1)
   Note: The T-maze was custom-built by members of our lab.
   
   
   Figure 1. T-Maze used for both variants of the CD task shown with (A) and without (B) the removable barrier is used to confine the rat to the start box during the intertrial interval
   
   
2. A wooden stool (height: 69 cm) with a plastic saucer (diameter: 38 cm) attached to the seat serves, as the start box, is positioned at the base of the maze. The start box is separated from the maze by a removable 6-cm tall wooden barrier
   
3. Three removable wooden floor inserts covered with black plastic mesh on one side and smooth wood on the other serve as conditional cues (Figure 2). The black mesh was glued to one side of the inserts with superglue, and consisted of 4 x 4 mm mesh squares. For the CDWM variant of the task, the central arm insert (74 x 8 cm) extends halfway from the start box to the T-intersection. For the CD_STANDARD variant of the task, the central arm insert (117 x 8 cm) covers the entire length of the central arm from the start box to the T-intersection. The three goal arm inserts, one large insert (61 x 8 cm) and two small inserts (26 x 8 cm) are placed at the ends of the goal arms next to the reward cups
   
   
   Figure 2. Removable wooden inserts shown mesh side up used for the CDWM (A) and CD_STANDARD (B) variants of the task, and close up view of the insert (C)
   
   
4. Black curtain, surrounding entire behavior room, 51 cm away from the maze
   
5. Distal cues taped to black curtain, 142 cm from the floor, located behind the start pedestal, left and right reward cups (Figure 3). The cues are a pink triangle (38.1 x 29.2 cm), a red X (40.6 x 35.6 cm) and a blue cube (43.2 x 41.9 cm) made out of colored tape
   
   
   Figure 3. Distal cues taped to the curtains that surround the maze above the reward cups (A) and above the start box (B)
   
   
6. Plastic cups (3 cm diameter; 1 cm depth) located at the end of each goal arm where chocolate sprinkles (4-5 pieces) are delivered. The caps were 20 oz. water/soda bottle caps
   
7. One 60 W incandescent lamp attached to the curtain track of the back middle wall, near the ceiling. The lamp is facing up towards the ceiling, therefore the room is dimly lit with no direct lighting on any portion of the maze
   

Procedure