Statistical analysis and modeling of neural data Lecture 5 Bijan Pesaran 19 Sept, 2007
Goals Recap last lecture – review Poisson process Give some point process examples to illustrate concepts. Characterize measures of association between observed sequences of events.
Poisson process
Renewal process Independent intervals Completely specified by interspike interval density Convolution to get spike counts
Characterization of renewal process Parametric: Model ISI density. –Choose density function, Gamma distribution: –Maximize likelihood of data No closed form. Use numerical procedure.
Characterization of renewal process Non-parametric: Estimate ISI density –Select density estimator –Select smoothing parameter
Non-stationary Poisson process – Intensity function
Conditional intensity function
Measures of association Conditional probability Auto-correlation and cross correlation Spectrum and coherency Joint peri-stimulus time histogram
Cross intensity function
Cross-correlation function
Limitations of correlation It is dimensional so its value depends on the units of measurement, number of events, binning. It is not bounded, so no value indicates perfect linear relationship. Statistical analysis assumes independent bins
Scaled correlation This has no formal statistical interpretation!
Corrections to simple correlation Covariations from response dynamics Covariations from response latency Covariations from response amplitude
Response dynamics Shuffle corrected or shift predictor
Joint PSTH
Questions Is association result of direct connection or common input Is strength of association dependent on other inputs