The overall goal of this protocol is to demonstrate optimized shaping and training procedures for fully automated visual cognitive tasks and simultaneous neural data acquisition in rats using a floor projection maze. This is achieved by integrating video tracking and neural data acquisition systems with a behavioral control system that is capable of delivering task relevant stimuli and intracranial reward according to the animal's behavior. After rats learn to hold a stationary ready position in the center of the arena, target images appear that require a relevant behavioral response according to the task rules.
Timestamped neural data for peri event analyses show neural correlates to the ready position, the onset of target image presentation, and other task relevant events. What's scraped about this technique is that the floor projection race takes advantage of behavioral and anatomical evidence that rats process visual information in their lower visual hemifield. Also, tasks designed in this apparatus take advantage of rat's natural tenancy to explore the environment.
Finally, a whole multitude of visually guided cognitive tasks can be designed to explore cognitive function In rodent models, We developed the floor projection maze for better validity and translational relevance for studies conducted in humans and non-human primates. This technique has a better application for understanding human disorders of memory and attention. Because these disorders involve processing of visual information.
The floor projection maze is an open field without walls. A rear projection screen serves as the floor of the apparatus. Any shape mazo arena can be placed on the floor, or virtual visual borders can be projected.
The rear projection screen floor is constructed of three layers. Dual vision fabric is stretched over a thick rectangular piece of plexiglass. A thin layer of plexiglass is placed over the fabric to protect the screen material sandwiching.
The screen material between thick, plexiglass underneath and thin plexiglass on top provides the most effective image projection below and to the side of the maze is a short throw projector, which back projects images onto the underside of the maze floor. An overhead camera attached to a computer with the Cineplex basic behavior module provides video tracking and online analysis of positional data. To follow the rat's position, either attach LEDs to the rat's head stage or track the OID of the rats contour With the video tracking system, the test arena for behavioral tasks placed on the plexiglass should be constructed of mat material.
When using the neural data acquisition system, ensure that the floor projection maze and the ICS system are grounded to the pre amplifier to minimize electrical noise. First habituate the rat to the behavioral room for 10 minutes with the equipment switched on, then return the rat to the colony on the next day. Repeat this.
Step on the third day, connect the ICS and head stage tethers to the rat and habituate the rat to the testing arena for 10 minutes. On the fourth day, determine the lowest ICS amplitude to establish a place preference. Using an informal place preference conditioning protocol.
Slowly increase pulse one and pulse two amplitudes until the rat is conditioned to the place where ICS reward occurs. Typical amplitude values are between 20 and 80 micro ampers. On day five and onward, deliver an ICS reward to train the rats to the ready area and to entry into the east and west image areas.
Continue the training until the rat is alternating between the two image areas. It is critical to train rats to maintain a stationary ready position in the ready area. The ready position controls from which direction the rat approaches the target images and the distances from which the rat views the presented images.
For the intermediate stage, introduce 50 decibels of white noise to signal the start of a trial. Turn off the white noise when the rat enters the ready area. Automate the delivery of an ICS reward to the rat for entering the ready area and for successfully completing the ready positions.
Gradually decrease the reward probabilities for entering the ready area and successful completion of ready positions to between zero and 10%At the same time, taper up the ready position. Latencies in 100 millisecond steps to train the rat to stop and wait in the ready position. At this stage of training, it is important not to over reward rats in the ready position because over training will result in delayed transition to late shaping and task specific rules.
If the rat prematurely breaks the ready position, turn on the white noise. The rat has to restart the trial on the opposite side of the arena. Move on to late shaping when the rat can reliably maintain the ready position for up to 1200 milliseconds for each trial.
A new ready position duration determines how long the rat must remain still before the target images appear. Training during late shaping is specific to the task and is automated in all task parameters. With the flexibility to manually deliver ICS rewards for the initial training in the visual by conditional discrimination task, train rats on a simple shape and luminance discrimination.
Begin the trial by turning on the white noise. Vary the required duration for the rat to remain in the ready position between trials. If a rat is not reliably maintaining a stationary ready position, deliver an ICS reward.
Manually present a pair of images in the image presentation area, pseudo randomly present the correct image on the left or right side of the image area. Deliver an ICS reward. When the rat approaches the correct image on the first day of training.
Only issue a 75 decibel burst of white noise as a deterrent for an incorrect response issue. A correction trial after an incorrect trial. Correction trials are carried out on the opposite side of the arena.
Use the same correct left or right side and ready Position latency as the previous incorrect trial. Once the rat successfully performed the simple luminance discrimination Introduce the bicon Conditional discrimination task. Do not issue noise bursts for incorrect trials.
For the bi conditional discrimination task, the correct image is determined by the floor pattern. For example, the black star is correct when the floor is striped and the white circle is correct. When the floor is gray, trials alternate between the east and west sides with the correct image presented.
Pseudo randomly on the left or right side of the image area implement correction trials following incorrect trials. For the visual spatial attention task Present gray circles at defined spatial locations. Begin the trial with white noise and turn it off When the rat enters the ready area.
After the rat holds the ready position for the required duration, illuminate the target circle by turning it white. Correct locations are assigned pseudo randomly. After the rat has successfully completed the ready position, illuminate a target circle and deliver an ICS reward.
When the rat approaches the correct circle within five seconds, if the rat approaches a different circle, no reward is delivered. The rat starts a new trial at the opposite side of the arena. If the rat fails to approach any circle within five seconds, score this as an omission trial.
Illuminate the whole floor and do not deliver a reward initially. Keep the target circle illuminated until the rat approaches it. As learning progresses gradually decrease the amount of time the target circle remains illuminated.
When the rat reaches 80%accuracy, decrease the illumination time on the target circle to one second and make no other changes. When the rat achieves 80%correct on the one second illumination condition, reduce the cue time to 500 milliseconds. Early shaping typically requires 100 to 150 trials for the rats to alternate between the east and west image areas of the arena.
During early shaping, the rats typically run through the ready area in the center of the arena and spend most of their time exploring the perimeter of the arena. For intermediate shaping, rats require 600 to 700 trials to reliably maintain the required stationary ready position. Their paths are stereotyped loops from the ready area to the image area.
With less time spent exploring the perimeter of the arena. By the end of intermediate shaping, rats reliably maintain a stationary ready position in the ready area. Before approaching the target visual stimulus, the rat then initiates the next trial on the opposite side of the arena.
At the end of late shaping single unit and local field potential activity were collected by the neural data acquisition system. In the postal cortex of rats performing the VBCD task cells increased their firing rate at the onset of the target presentation and decreased at the onset of the floor pattern presentation. In the posterior parietal cortex of rats performing the VSA task cells increased their firing rate in response to the circle illumination.
And when the rat approached the target circle in the VSA task, while the rats were in the ready position before the circle illumination local field potential activity in the posterior parietal cortex. During performance in the VSA task showed strong power in the theta range at about eight hertz. By following these shaping and training protocols, one can design multitude of tasks to explore cognitive function and visual processing in rodent models.
This technique provides a sophisticated behavioral paradigm for researchers in the field of learning memory and attention that provide better translational relevance of findings in rodent models to humans.
