FT_DATATYPE_SPIKE
Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_datatype_spike”.
FT_DATATYPE_SPIKE describes the FieldTrip MATLAB structure for spike data Spike data is obtained using FT_READ_SPIKE to read files from a Plexon, Neuralynx or other animal electrophysiology data acquisition system. It is characterised as a sparse point-process, i.e. each neuronal firing is only represented as the time at which the firing happened. Optionally, the spike waveform can also be represented. Using this waveform, the neuronal firing events can be sorted into their single units. A required characteristic of the SPIKE structure is a cell-array with the label of the (single or multi) units. label: {'unit1' 'unit2' 'unit3'} The fields of the SPIKE structure that contain the specific information per spike depends on the available information. A relevant distinction can be made between the representation of raw spikes that are not related to the temporal strucutre of the experimental design (i.e trials), and the data representation in which the spikes are related to the trial. For a continuous recording the SPIKE structure must contain a cell-array with the raw timestamps as recorded by the hardware system. As example, the original content of the .timestamp field can be timestamp: {[1x504 uint64] [1x50 uint64] [1x101 uint64]} An optional field that is typically obtained from the raw recording contains the waveforms for every unit and label as a cell-array. For example, the content of this field may be waveform: {[1x32x504 double] [1x32x50 double] [1x32x101 double]} If the data has been organised to reflect the temporal structure of the experiment (i.e. the trials), the SPIKE structure should contain a cell-array with the spike times relative to an experimental trigger. The FT_SPIKE_REDEFINETRIAL function can be used to reorganise the SPIKE structure such that the spike times are expressed relative to a trigger instead of relative to the acquisition devices internal timestamp clock. The time field then contains only those spikes that ocurred within one of the trials . The spike times are now expressed on seconds relative to the trigger. time: {[1x504 double] [1x50 double] [1x101 double]} In addition, for every spike we register in which trial the spike was recorded: trial: {[1x504 double] [1x50 double] [1x101 double]} To fully reconstruct the structure of the spike-train, it is required that the exact start- and end-point of the trial (in seconds) is represented. This is specified in a nTrials x 2 matrix. trialtime: [100x2 double] As an example, FT_SPIKE_MAKETRIALS could result in the following SPIKE structure that represents the spikes of three units that were observed in 100 trials: label: {'unit1' 'unit2' 'unit3'} timestamp: {[1x504 double] [1x50 double] [1x101 double]} time: {[1x504 double] [1x50 double] [1x101 double]} trial: {[1x504 double] [1x50 double] [1x101 double]} trialtime: [100x2 double] sampleinfo: [100x2 double] waveform: {[1x32x504 double] [1x32x50 double] [1x32x101 double]} waveformdimord: '{chan}_lead_time_spike' cfg For analysing the relation between the spikes and the local field potential (e.g. phase-locking), the SPIKE structure can have additional fields such as fourierspctrm, lfplabel, freq and fourierspctrmdimord. For example, from the structure above we may obtain label: {'unit1' 'unit2' 'unit3'} timestamp: {[1x504 double] [1x50 double] [1x101 double]} time: {[1x504 double] [1x50 double] [1x101 double]} trial: {[1x504 double] [1x50 double] [1x101 double]} trialtime: [100x2 double] waveform: {[1x32x504 double] [1x32x50 double] [1x32x101 double]} waveformdimord: '{chan}_lead_time_spike' fourierspctrm: {504x2x20, 50x2x20, 101x2x20} fourierspctrmdimord: '{chan}_spike_lfplabel_freq' lfplabel: {'lfpchan1', 'lfpchan2'} freq: [1x20 double] Required fields: - label - timestamp Optional fields: - unit - time, trial, trialtime - waveform, waveformdimord - fourierspctrm, fourierspctrmdimord, freq, lfplabel (these are extra outputs from FT_SPIKETRIGGEREDSPECTRUM and FT_SPIKE_TRIGGEREDSPECTRUM) - hdr - cfg Deprecated fields: - origtime, origtrial Obsoleted fields: - <unknown> Revision history: (2012) Changed the dimensionality of the waveform to allow both stereotrode and tetrode data to be represented. (2011/latest) Defined a consistent spike data representation that can also contain the Fourier spectrum and other fields. Use the xxxdimord to indicate the dimensions of the field. (2010) Introduced the time and the trialtime fields. (2007) Introduced the spike data representation. See also FT_DATATYPE, FT_DATATYPE_RAW, FT_DATATYPE_FREQ, FT_DATATYPE_TIMELOCK