Wedge analysis

Purpose

Wedge analysis is used to analyze whether there is differential growth or retraction of dendritic processes in particular locations in virtual/anatomical regions by examining the distribution of dendritic length relative to a fixed point and direction. It is similar to the Polar Histogram, although the Wedge analysis determines direction relative to a single point, while the Polar Histogram determines direction locally.

How it works

A coordinate system is created at the point with the 0 angle defined by a ray that originates at the point. The plane is divided into a number of equiangular wedges. The length in each wedge is the sum of the lengths that fall within the wedge. Projection causes foreshortening of the tracing because the Z information is lost in projection but length calculations still take the Z information into account. The total length in all wedges is the same as the total length of all dendritic processes used in the analysis.

Procedure

  1. Prepare your data file in Neurolucida or Neurolucida 360.
    1. Open your data file in Neurolucida or Neurolucida 360.
    2. Open a wedge sample file:
      1. Click Open Data File from the File menu.
      2. Check Merge at the bottom of the window .
      3. Select one of the sample wedge files (e.g., WEDGE08.ASC) from the Neurolucida or Neurolucida 360 directory. The number in the file name refers to the number of wedges (e.g., 8 wedges for WEDGE08) or 8 spokes in 2D.
      4. Click OK. The wedge tool is displayed over the tracing .

    3. Move the wedge tool to an appropriate location:

      1. Switch to Edit mode.
      2. Click the wedge tool to select it.
      3. Right-click away from the wedge tool and select Move Selected Contour.
      4. Drag the center of the wedge tool to change its location.
    4. Change the direction of the wedge tool:
      1. Switch to Edit mode.
      2. Click the wedge tool to select it.
      3. Right-click away from the wedge tool and select Rotate Selected Contour.
      4. Drag the tip of the arrow.
    5. Save and close the data file.

     

  2. Open your data file in Neurolucida Explorer.

  3. Select Wedge Analysis from the Spatial dropdown menu on the Analyze ribbon to open the Wedge Analysis window.

Reference

Nogueira-Campos, A. A., Finamore, D. M., Imbiriba, L. A., Houzel, J. C., & Franca, J. G. (2012). Distribution and morphology of nitrergic neurons across functional domains of the rat primary somatosensory cortex. Frontiers in Neural Circuits, 6, 57. http://doi.org/10.3389/fncir.2012.00057

Goldstein, L.A., Kurz, E.M., Kalkbrenner, A., Sengelaub, D.R. (1993). Changes in dendritic morphology of rat spinal motoneurons during development and after unilateral target deletion. Developmental Brain Research, 73:151-163.

In this article, wedges are referred to as "sectors" but the conceptual basis is the same.