Knowledge Base

Data Analysis

Data Preparation

Track Smoothing

Choose Acquisition > Track Smoothing Profile.

• Lowess Smoothing: Select to remove the effect of body wobble. When the animal sits still on the platform, yet the body center-point still moves slightly due to system noise, this results in an overestimation of, for example, the total distance moved.
• Minimal Distance Moved: Select to only measure the total distance moved over the time periods in which the animal was really swimming.

Analysis Profiles

Choose Analysis > Analysis Profile.

The template experiment contains five analysis profiles:

• Latency to Reach Platform: This profile contains the variable Latency to platform to calculate how long it takes the animal to find the platform. You can use the variable Distance to zone to calculate Gallagher's index (Gallagher et al., 1993). The variable In quadrants calculates the frequency and duration of visits to each quadrant.
• Path Shape: The path shape can be determined by using the variables Turn angle, Angular velocity and Meander.
• Whishaw's Corridor (only present if you chose a zone template with corridors when creating the experiment): The variable Inside Whishaw's Corridor calculates the time the animal spent inside any of Whishaw's corridors. The variable Outside Whishaw's Corridor calculates the time the animal spent outside any of Whishaw's corridors.
• Distance & Time: In this profile, the total Distance Moved and the mean Velocity and the group means with their standard errors are calculated.
• Heading: In this profile, the mean Heading to each of the platforms is calculated.

Swim Patterns

Thigmotaxis (Wall-Hugging Swim)

This is a persistent swim along the wall of the pool that could include sporadic swims toward the center of the pool. To quantify thigmotaxis, calculate the time spent in the Thigmotaxis zone relative to the total track duration.

Random Search

This is swimming over the entire area of the pool in straight swims (zig-zag pattern), or in wide circular swims.

Divide the pool into quadrants or smaller zones, then count the number of times each zone was visited and the time in zones. If zone visits and time are uniformly distributed across zones, the search pattern could be said to be random or at least covering the whole pool.

Scanning

The search path is restricted to a limited, often central, area of the pool. Perform the same analysis as for random search, but covering only the area and zones towards the center (see Figure 1C in Janus C. 2004. Learning and Memory: 337–346). Relate this to the time in the external zones.

Chaining/Serial Visits

This is circular swimming (in anticlockwise or clockwise direction) at a fixed distance from the wall, in which the escape platform was located. To quantify chaining, draw a specific circular crown zone. Calculate the time spent in this zone versus the time in the rest of the arena, or calculate rotations occurring in that zone.

Focal Search

This is searching in a restricted area of the pool, usually the target quadrant. The path is characterized by a directional, straight swim to a specific area followed by dense concentration of superimposed loops and turns there.

• To detect rapid changes in direction, use the Multi condition dependent variable to define your criterion, for example Absolute Meander > 10 degrees/cm. This marks the time when Meander is greater than the threshold value.
• Combine Meander with an In zone variable in a Free Interval to select the time from when the rapid change in direction occurs to when the subject enters the target area.

In the Arena Settings, define a zone around the platform or any other target point, and name it Focal zone. In the Analysis profile, define a Free interval with:

• Interval Start: Meander: Absolute Meander > 10 degree/cm
• Interval Stop: In zone: Center point is in Focal zone

Direct Swim Path

This is the direct swim path to the location containing the escape platform. Define an In zone variable based on the Whishaw's corridor to calculate the time spent in and outside this corridor before reaching the platform. See also the EthoVision XT Help.

Floating

A state of inactivity without forward movement. The plotted path is short, often with thick or tight sections caused by non-directional drift. Quantify floating with Movement (Not moving) or a Multi condition that includes Movement (Not moving) and In zone (Center point is not near the wall of the pool; define a dedicated zone if necessary).

Gallagher's Proximity Score

Cumulative Search Error (For Training Trials)

Gallagher et al. (1993) proposed the Cumulative search error to provide information about the spatial distribution of the animal's search during training trials. This is obtained by sampling the position of the animal in the water maze 10 times per second, and calculating the averages of distance to the platform for 1-second periods. The averages are then summed up.

In EthoVision XT, you have two options:

• Calculate the Total Distance from the Platform:

  In the Analysis profile, choose the dependent variable Distance to zone, with the Statistic Total. This equals the "true" Gallagher's Cumulative search error when sample rate = 10 samples/s. In most cases the Total distance from the platform highly correlates with the "true" search error.

• Calculate the "True" Gallagher's Cumulative Search Error:
  1. In the Data profile, select time bins (1 second).
  2. In the Analysis profile, define the dependent variable Distance to zone, with the Statistic Mean.
  3. Choose Analysis > Results > Statistics and Charts, click Calculate, then export the results via Analysis > Export > Statistics.
  4. In Excel, open the export file and sum up the average values per trial.

Average Search Error (For Probe Trials)

According to Gallagher et al. (1993), the Average search error is obtained by calculating the average distance of the animal to the platform location over 1-second intervals, and then averaging the results.

Source: EthoVision XT 18 - Application Manual, Noldus Information Technology