Files & Formats

Neuroelectrics devices generate a series of files and formats. Proprietary ones are in bold:

- The .easy data format (ASCII, plain text) 
- The .info file (ASCII, plain text)
- The .edf (EDF+) and ".nedf" data formats (binary)
- The .stim file (ASCII, plain text)
- The .sdeeg SD card data format (binary)

In general, time keeping is given with time stamps per sample in ms since Jan 1st 1970 (Unix time).

Stimulation generated files

Neuroelectrics stimulation StarStim class devices generate stimulation specific files as well as EEG data. Here we describe the former (for EEG see the EEG data section).

the .info file associated with a stimulation session

Here is an example of the ASCII data file associated to a stimulation session. The name of the file would be something like '20130220112635_Patient01.info:

StartDate (first EEG timestamp): 1361377909087 
Device class: StarStim
Device Mac: 00:07:80:58:9C:1A
NIC version: v1.1.9
Firmware version: 699
Line filter status: OFF
Additional channel status:OFF
Number of records of Stimulation: 46 (1 second/record)
Total number of channels: 8
Number of EEG channels: 6
Number of stimulation channels: 1
Stimulation sampling rate: 500 Samples/second
Stimulation units: uA
Ramp up duration (s): 15
Ramp down duration (s): 15
Shamp ramp duration (s): OFF
Stimulation duration (s): 1200
Type of stimulation: tACS+
Stimulation parameters:
Channel 1: 
 Position: C3
 Type: EEG Recording
 Channel 2: 
 Position: C4
 Type: Stimulation Anodal
 Amplitude (uA): 100
 Offset (uA): 0
 Frequency (Hz): 10
 Channel 3: 
 Position: Ch3
 Type: EEG Recording
Channel 4: 
 Position: Ch4
 Type: Return
 Percentage return: 100%
Channel 5: 
 Position: Ch5
 Type: EEG Recording
 Channel 6: 
 Position: Ch6
 Type: EEG Recording
Channel 7: 
 Position: Ch7
 Type: EEG Recording
 Channel 8: 
 Position: Ch8
 Type: EEG Recording
Trigger information:
 Code	Description
 1	Subject moved
 2	Eyes opened
 3	Eyes closed
 4	sleeping
 5	EEG signals are noisy
 6	
 7	
 8	
 9

the .stim file

This ASCII file contains a record of the currents at each electrode.

There is a row per time sample with one column per channel (units in uA).

The last column contains the time stamps per sample in ms since Jan 1st 1970 (Unix time).

Here is the typical content of a .stim file. There are 8 columns (one per channel). Channels with a constant value of -1 identify channels not used for stimulation (they would be used for EEG). The first two columns provide injected current in uA, with a + sign indicating injection of current into the scalp. The last column is the Unix timestamp (ms).

246	-246	-1	-1	-1	-1	-1	-1	1381762713753
246	-246	-1	-1	-1	-1	-1	-1	1381762713754
246	-246	-1	-1	-1	-1	-1	-1	1381762713755
246	-246	-1	-1	-1	-1	-1	-1	1381762713756
246	-246	-1	-1	-1	-1	-1	-1	1381762713757
247	-247	-1	-1	-1	-1	-1	-1	1381762713758
247	-247	-1	-1	-1	-1	-1	-1	1381762713759
247	-247	-1	-1	-1	-1	-1	-1	1381762713760
247	-247	-1	-1	-1	-1	-1	-1	1381762713761
247	-247	-1	-1	-1	-1	-1	-1	1381762713762
247	-247	-1	-1	-1	-1	-1	-1	1381762713763
248	-248	-1	-1	-1	-1	-1	-1	1381762713764
248	-248	-1	-1	-1	-1	-1	-1	1381762713765

EEG data files and formats

the .info file associated with an EEG only session

Here is an example of what this plain text file contains. The name of the file would be something like '20131011141257_demo.info:

StartDate (first EEG timestamp): 1381493577260
Device class: Enobio20
Device MAC: 00:07:80:63:F0:CD
NIC version: v1.2.9
Firmware version: 699
Line filter status: 60 Hz
Additional channel status: OFF
Total number of channels: 20
Number of EEG channels: 20
Number of records of EEG: 15381
Number of packets lost: 0(0.00%)
EEG sampling rate: 500 Samples/second
EEG units: nV
EEG montage:
 Channel 1: P7
 Channel 2: P4
 Channel 3: Cz
 Channel 4: Pz
 Channel 5: P3
 Channel 6: P8
 Channel 7: O1
 Channel 8: O2
 Channel 9: T8
 Channel 10: F8
 Channel 11: C4
 Channel 12: F4
 Channel 13: Fp2
 Channel 14: Fz
 Channel 15: C3
 Channel 16: F3
 Channel 17: Fp1
 Channel 18: T7
 Channel 19: F7
 Channel 20: EXT
Number of records of Accelerometer: 30 (1 second/record)
Number of channels of Accelerometer: 3
Accelerometer sampling rate: 100 Samples/second
Accelerometer units: mm/s^2
Trigger information:
 Code	Description
 1	EventA
 2	EventB
 3	Movement
 4	Eyeblink
 5	
 6	
 7	
 8	
 9

The .easy data format (ASCII)

 ABOUT THE NE ASCII DATA FORMAT (July 2012): 
       NE ASCII files contain one line per time sample. Each line contains
       first the EEG data (8 or 20 channels, depending on the device, with
       units in nV), followed by  three acceleration channels (aX,aY,aZ 
       in mm/s^2- millimeters per second squared), an *optional* external 
       input channel, a trigger flag (int32) and, finally, 
       a timestamp in Unix time (ms from Jan 1 1970):

 Ch1(nV) ... Ch8or20(nV) aX(mg) aY(mg) aZ(mg) AddSensor Flags(uint32) TimeStamp (ms)
   
 Therefore Enobio8/StarStim will have a minimum of 8+2 (10) columns, or 8+3=11 if no 
   accelerometer or >= 8+4 (with accelerometer). In summary:

   Enobio8/20
        10 Columns: no AddSensor, no accelerometer data:
        11 Comumns: no accelerometer, but there is AddSensor
        13 Columns: there is accelerometer, but no Addsensor
        14 Comumns: there is accelerometer, AddSensor.

   Enobio 20 will have >= 22 and >=24 columns if acc. data present:
        22 Columns: no AddSensor, no accelerometer
        23 Comumns: no accelerometer, but there is AddSensor
        25 Columns: there is accelerometer, no AddSensor 
        26 Comumns: there is accelerometer, AddSensor.

   Enobio 32 will have >=34 and >=36 if acc data is present
        34 Columns: no AddSensor, no accelerometer
        35 Comumns: no accelerometer, but there is AddSensor
        37 Columns: there is accelerometer, no AddSensor 
        38 Comumns: there is accelerometer, AddSensor.

Here is an example from a StarStim device (8 Channels) where the first 4 channels are used for stimulation (with "-1"s), and with accelerometer data (3 channels), markers and timestamp:

-1	-1  8999110  29602960	 27793792  19921829  -3670597	18110801	  -2745  9561	 -912  0  1353011252736
-1	-1  8902360  29539254	 27764085  19818737  -3924179	18143799	  -2745  9561	 -912  0  1353011252738
-1	-1  8827496  29457477	 27727511  19748117  -4140377	18101551	  -2745  9561	 -912  0  1353011252740
-1	-1  8779812  29376462	 27720311  19705727  -4315472	18054868	  -2745  9561	 -912  0  1353011252742

The .edf (binary, EDF+) data format

This is the standard | EDF data format. Files in this format can be opened from EDF data readers as well as with NIC Offline (and exported/saved into any of the other NE formats). The EDF+ format has only 16 bits of quantization. To avoid any distortion of the signal the EDF+ files are pre-processed including:

- High pass filtering of the signal at 0.1 Hz

- Clipping of the signal at [-32.767mV, 32.767mV]

The .nedf (binary) data format

This is Neuroelectrics proprietary data format (NEDF). It is lossless (full 24 bit) binary. It can be opened by NIC Offline and exported/saved into any of the other NE formats. Additionally, at section Data_Processing_with_Matlab#Working_with_NEDF_files you can also find Matlab code to open NEDF files.

The .sdeeg SD card data

This is another proprietary, binary data format. It can be opened with NIC Offline software and exported/saved into any of the other NE formats.