add first section bep006 spec

src/04-modality-specific-files/06-electroencephalography.md

@@ -8,3 +8,59 @@ academic literature:
 > Oostenveld, R. (2018, December 6). BIDS-EEG: an extension to the Brain
 > Imaging Data Structure (BIDS) Specification for electroencephalography.
 > [https://doi.org/10.31234/osf.io/63a4y](https://doi.org/10.31234/osf.io/63a4y)
+
+## EEG recording data
+
+Template:
+
+```Text
+sub-<label>/
+    [ses-<label>]/
+      eeg/
+        sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>]_eeg.<manufacturer_specific_extension>
+        sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>]_eeg.json
+        sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>]_channels.tsv
+        sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>]_electrodes.tsv
+        sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>]_coordsystem.json
+        sub-<label>[_ses-<label>]_task-<label>[_acq-<label>][_run-<index>]_photo.jpg
+
+```
+
+While there are many file formats to store EEG data, there are two officially
+supported data formats in EEG-BIDS: The [European data format](https://www.edfplus.info/)
+(`.edf`), and the [BrainVision data format](https://www.brainproducts.com/productdetails.php?id=21&tab=5)
+(`.vhdr`, `.vmrk`, `.eeg`) by Brain Products GmbH. There are also two
+*unofficial* data formats that are currently accepted: The format used by the
+MATLAB toolbox [EEGLAB](https://sccn.ucsd.edu/eeglab) (`.set` and `.fdt` files)
+and the [Biosemi](https://www.biosemi.com/) data format (`.bdf`). The original
+data format, if different from the supported formats, can be stored in the
+`/sourcedata` directory.
+
+The original data format is especially valuable in case conversion elicits the
+loss of crucial metadata specific to manufacturers and specific EEG systems. We
+also encourage users to provide additional meta information extracted from the
+manufacturer specific data files in the sidecar JSON file. Other relevant files
+MAY be included alongside the EEG data.
+
+Note that for proper documentation of EEG recording metadata it is important to
+understand the difference between electrode and channel: An EEG electrode is
+attached to the skin, whereas a channel is the combination of the analog
+differential amplifier and analog-to-digital converter that result in a
+potential (voltage) difference that is stored in the EEG dataset. We employ
+the following short definitions:
+
+- Electrode = A single point of contact between the acquisition system and the
+  recording site (e.g., scalp, neural tissue, ...). Multiple electrodes can be
+  organized as caps (for EEG), arrays, grids, leads, strips, probes, shafts,
+  etc.
+- Channel = A single analogue-digital-converter in the recording system that
+  regularly samples the value of a transducer, which results in a signal being
+  represented as a time series in the data. This can be connected to two
+  electrodes (to measure the potential difference between them), a magnetic
+  field or magnetic gradient sensor,  temperature sensor, accelerometer, etc.
+
+Although the "reference" and "ground" are often referred to as channels, they
+are in most common EEG systems not amplified and recorded by themselves, and
+therefore should not be represented as channels but as electrodes. The type of
+referencing and optionally the location of the reference electrode and the
+location of the ground electrode MAY be specified.