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MPM System Setup screen has new target images (calibration blocks) for larger adult mouse and adult rat. 

The upcoming Pathfinder MPM Software V2.8.5 release for the Multi-Probe Micromanipulator (MPM) System includes two additional target images (also called calibration blocks) for system setup.

What are target images?

Bregma and Lambda define the stereotactic coordinate system used by the MPM System. The target image is used to calibrate the system in simulation mode. This mode is useful for system setup, as well as for practicing calibration before using a real test subject.

Calibration is done by using course and fine stepping of the motorized manipulators to move the calibration probe until its tip touches Bregma on the target image, capturing the tip position in the software, and repeating for Lambda.  All additional manipulators in the rig need only touch Bregma.

In the current MPM System software, the default target image Adult Mouse is an adult mouse skull with a 3 mm separation between Bregma and Lambda.

Larger adult mouse target

Based on user feedback, the upcoming Pathfinder V2.8.5 release includes a new mouse target image, Adult Mouse 4.1, with a more realistic separation of 4.1 mm between Bregma and Lambda. This is the best average separation, based on statistical studies with a large sample. This separation is used in the standard for the Allen Common Coordinate Framework (CCF) brain atlas used by Andy Peters’ (Peters Lab, Oxford) Neuropixels Trajectory Explorer (NTE) and Dan Birman’s (Steinmetz Lab, University of Washington) Pinpoint planning systems.

Scaling the target for use with Neuropixels Trajectory Explorer (NTE)

While 4.1 mm is a good average number, each individual mouse will exhibit different values, depending on the size of the mouse. After touching Bregma and Lambda in the physical experiment, Pathfinder will record the actual Bregma – Lambda separation for this experiment. Then, in the NTE system, the Allen CCF atlas will be scaled based on this separation. Therefore, the atlas will be as close as possible to the true representation for this experiment.

Adult rat target

While most MPM System users work with mice, there is growing interest in using the micromanipulator on larger subjects, such as adult rats. Pathfinder release V2.8.5  includes a new target image, Adult Rat, with 10 mm separation between Bregma and Lambda. This target is based on a ~640g rat.

With this larger skull, careful initial positioning of the neural probes is essential in order to get enough travel from the motorized stages for probe insertions. Setting the coarse positioning so the probe is midway between Bregma and Lambda generally allows ample travel remaining in the stages.

This feature was suggested by David Herr and Garyn Jung, Neurological and Endocrine Toxicology Branch, US EPA.

New Scale MPM System probe viewer window with the new Adult Rat skull target image

MPM System probe viewer screen with the new Adult Rat target image (calibration block) for electrophysiology research with adult rats