# Sessions

A session is an object that makes the link between your application and an EMOTIV headset. When the user wants to work with a headset, your application should create a session first.\
Then you can:

* subscribe to the [data stream](https://emotiv.gitbook.io/cortex-api/data-subscription) of the headset
* create a [record](https://emotiv.gitbook.io/cortex-api/records) and add [markers](https://emotiv.gitbook.io/cortex-api/markers)
* use [BCI](https://emotiv.gitbook.io/cortex-api/bci)

Your application can open only one session at a time with a given headset. But it can open multiple sessions with multiple headsets.

## Session lifetime

A session is created by [createSession](https://emotiv.gitbook.io/cortex-api/session/createsession) and closed by [updateSession](https://emotiv.gitbook.io/cortex-api/session/updatesession).

A session is linked to an application. All the sessions of an application are automatically closed when the application is disconnected from the Cortex service. A session is also closed if the headset is disconnected.

A session is a **temporary in-memory object**, it is not persistent. After a session is closed, it is destroyed by Cortex. If you want to create a persistent object, please [create a record](https://emotiv.gitbook.io/cortex-api/records/createrecord) inside your session.\
See [Records](https://emotiv.gitbook.io/cortex-api/records) for details.

## Session activation

When you create a session, you can activate it or leave as is.

If the session is not activated, then it doesn't use the license of the user. You cannot subscribe to the EEG stream and you are limited to the low resolution performance metrics. You can neither create a [record](https://emotiv.gitbook.io/cortex-api/records) nor [markers](https://emotiv.gitbook.io/cortex-api/markers).

If the session is activated, then it uses the license of the user. Depending on the license scope of the license, you can subscribe to the EEG stream or high resolution performance metrics. If the license has a session quota, then this session will be debited from this quota.

Use [querySessions](https://emotiv.gitbook.io/cortex-api/session/querysessions) and check the field **status** to know if a session was activated or not.