Smart: Testing for "Global Motor Activity"

SMART offers two main ways to analyse motor-activity-related behaviours: on one hand, allows for the determination of the position co-ordinates of the experimental subject along time in the plane defined by the observation scenery. Using this kind of approach, common to all the systems offering video based analysis of behaviour, information about distance travelled, velocity, time spent into specific position, etc., can be easily derived.
Besides this, SMART cans also determinate motor activity as a measure of the amount of change between successive digital images. To do this, each new image is compared with their preceding and the number of pixels whose luminance level change above a user-defined threshold level is obtained. This number reflects motor activity, as the only source of change is the displacement of the experimental subject into the working scenery, provided the elimination of random changes in luminance by the threshold filter.
The number of changing pixels is dependent on the amount of motor activity produced, but in its value there is no indication of the source of the activity as an individual entity. The number of changing pixels can be expressed as a % of the total area covered by the scenery, in such as way that the area (of change) along time become a direct measure of motor activity.

Spatial filters allow for the classification of movements as fast or slow; resting time is also cumulated separately.

Computer screen when a determination of Global Motor Activity is being carried outFigure 6 shows the appearance of the computer screen when a determination of "Global Motor Activity" is being carried out. In the video image zone (left of the screen), a square-shaped open field is shown; nine zones have been defined, in order to obtain periphery versus central activity, activity per quadrant, etc.
In the left side of the screen, the current result are shown: a bar graph associated to each zone (according to its respective colour), shows the activity being detected in each one of them (higher in the zone 2, generated by the animal moving in it). The pie chart summarises the total activity detected in the whole scenery. The timers below the pie show total time resting, moving slow and moving fast.
In the middle part of the left side of the screen, the Start/Stop/Reset buttons allows for the control of the experiment. A timer shows the total elapsed time. Below this, is the Time Control; it will be described separately.
For smoothing the shape of the activity signal, one activity value is obtained each 0.5 s, as the mean of 5 samples. At user selected time periods, the mean activity detected is presented zone by zone and for the total (see active window in figure 7). It is very important to note that as this analysis is done in real time on the current inputting images; data can not be re-obtained unless stored on videotape.

Data output from the global activity monitorFigure 7. Data output from the global activity monitor.This approach to motor activity measurement can be very useful for the evaluation of the amount of movement along time. It has a clear advantage over the devices traditionally used for this purpose either based on capacitive/inductive changes or IR beams cuts. Unlike the firsts, SMART is much more precise and their output reflects exactly the amount of movement; capacitive and inductive devices can not be calibrated easily as SMART. IR devices offers a solution in some way similar to those offered by SMART, but with an enormous difference in spatial resolution. While standard IR sensor are usually 45 x 45 cm, with 16 IR beams 2.5 cm spaced, if SMART is used in a equally sized field, its resolution is less than 1 mm, 25 times higher!
Combining zones definition with global activity evaluation, interesting applications can be developed. For instances, it is possible to evaluate activity in several cages at the same time (defining each cage as a different zone); this could make possible to test, simultaneously, as many cages as wanted, with the only limit of an adequate spatial resolution. If four 45 x 45 cm arenas are assigned to 250 x 250 pixels zones, resolution is 1.8 mm/pixel, still very high.

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