title: Second spatial derivative analysis of cortical surface potentials recorded in cat primary auditory cortex using thin film surface arrays: Comparisons with multi-unit data.
abstract: Current source density analysis of recordings from penetrating electrode arrays has traditionally been used to examine the layer- specific cortical activation and plastic changes associated with changed afferent input. We report on a related analysis, the second spatial derivative (SSD) of surface local field potentials (LFPs) recorded using custom designed thin-film polyimide substrate arrays.
  
  
  
  SSD analysis of tone- evoked LFPs generated from the auditory cortex under the recording array demonstrated a stereotypical single local minimum, often flanked by maxima on both the caudal and rostral sides. In contrast, tone-pips at frequencies not represented in the region under the array, but known (on the basis of normal tonotopic organization) to be represented caudal to the recording array, had a more complex pattern of many sources and sinks.
  
  
  
  Compared to traditional analysis of LFPs, SSD analysis produced a tonotopic map that was more similar to that obtained with multi-unit recordings in a normal-hearing animal. Additionally, the statistically significant decrease in the number of acoustically responsive cortical locations in partially deafened cats following 6 months of cochlear implant use compared to unstimulated cases observed with multi-unit data (p=0.04) was also observed with SSD analysis (p=0.02), but was not apparent using traditional analysis of LFPs (p=0.6).
  
  
  
  SSD analysis of surface LFPs from the thin-film array provides a rapid and robust method for examining the spatial distribution of cortical activity with improved spatial resolution compared to more traditional LFP recordings.
authors.affiliation: Bionics Institute, Melbourne, Victoria, Australia; Department of Otolaryngology, University of Melbourne, Melbourne, Victoria, Australia; Medical Bionics Department, University of Melbourne, Melbourne, Victoria, Australia. Electronic address: jfallon@bionicsinstitute.org.
authors.forename: James B
authors.initials: JB
authors.lastname: Fallon
authors.affiliation: Bionics Institute, Melbourne, Victoria, Australia.
authors.forename: Sam
authors.initials: S
authors.lastname: Irving
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, CA, United States.
authors.forename: Satinderpall S
authors.initials: SS
authors.lastname: Pannu
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, CA, United States.
authors.forename: Angela C
authors.initials: AC
authors.lastname: Tooker
authors.affiliation: Bionics Institute, Melbourne, Victoria, Australia; Department of Otolaryngology, University of Melbourne, Melbourne, Victoria, Australia; Medical Bionics Department, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Wise
authors.affiliation: Bionics Institute, Melbourne, Victoria, Australia; Medical Bionics Department, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Robert K
authors.initials: RK
authors.lastname: Shepherd
authors.affiliation: Bionics Institute, Melbourne, Victoria, Australia.
authors.forename: Dexter R F
authors.initials: DR
authors.lastname: Irvine
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D001303:Auditory Cortex / Q000502:physiology* / Q000503:physiopathology; D001307:Auditory Perception / Q000502:physiology*; D002415:Cats; D003054:Cochlear Implants; D003638:Deafness / Q000503:physiopathology / Q000534:rehabilitation; D004195:Disease Models, Animal; D004567:Electrodes, Implanted; D004867:Equipment Design; D005072:Evoked Potentials, Auditory; D007612:Kanamycin; D012815:Signal Processing, Computer-Assisted
chemical_list: D007612:Kanamycin
keywords: Cochlear implant; Cortical plasticity; Local field potential; Neural prosthesis; Sensorineural hearing loss