# Mouse\_connectivity\_cache difference between structures in experiment dataframe

**URL:** <https://community.brain-map.org/t/mouse-connectivity-cache-difference-between-structures-in-experiment-dataframe/629>\
**Category:** Technical\
**Tags:** software, experiment-design, atlas-mouse-brain-connectivity, analysis, allensdk\
**Created:** [July 9, 2020, 3:40pm UTC](https://community.brain-map.org/t/mouse-connectivity-cache-difference-between-structures-in-experiment-dataframe/629 "2020-07-09T15:40:52Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![lemphi97](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@lemphi97](https://community.brain-map.org/u/lemphi97)\
**Post date:** [July 9, 2020, 3:40pm UTC](https://community.brain-map.org/t/mouse-connectivity-cache-difference-between-structures-in-experiment-dataframe/629/1 "2020-07-09T15:40:52Z")

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I would like to know what is the difference between `structure_id` and `primary_injection_structure` for an experiment. Most of the time, they are the same, but sometime they do differ.

Here’s an example for the experiment 527712447  
 ![image](https://canada1.discourse-cdn.com/flex027/uploads/brainobservatory/original/1X/6988b91adb5c6b7e5adf2de3f1823b6855417884.png)

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<div class="post-metadata">

**Author:** ![lemphi97](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@lemphi97](https://community.brain-map.org/u/lemphi97)\
**Post date:** [July 11, 2020, 2:39am UTC](https://community.brain-map.org/t/mouse-connectivity-cache-difference-between-structures-in-experiment-dataframe/629/2 "2020-07-11T02:39:48Z")

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In short, I don’t get what `primary_injection` imply. If someone could clarify.

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**Author:** ![wayne](https://yyz1.discourse-cdn.com/flex027/user_avatar/community.brain-map.org/wayne/32/16_2.png) [@wayne](https://community.brain-map.org/u/wayne)\
**Post date:** [July 13, 2020, 4:14pm UTC](https://community.brain-map.org/t/mouse-connectivity-cache-difference-between-structures-in-experiment-dataframe/629/3 "2020-07-13T16:14:43Z")

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Hello. Since these injections are not so precise that they can target only a single structure, we report which structure got the majority of the injection, as well as any other structures that also received some of the injection.

From the “Injection Site Polygon Drawing and Informatics Processing” section of the project overview document available [here](http://help.brain-map.org/download/attachments/2818171/Connectivity_Overview.pdf?version=2&modificationDate=1489022310670&api=v2) :  
“The structure receiving the largest proportion of signal intensity was distinguished as the primary structure, and all other structures were considered secondary structures. A quantified injection summary is provided for each image series that shows the relative amounts of signal detected within each  
infected structure.”