title: Dense arrays of micro-needles for recording and electrical stimulation of neural activity in acute brain slices.
abstract: OBJECTIVE
  This paper describes the design, microfabrication, electrical characterization and biological evaluation of a high-density micro-needle array. The array records from and electrically stimulates individual neurons simultaneously in acute slices of brain tissue.
  
  
  METHODS
  Acute slices, arguably the closest in-vitro model of the brain, have a damaged surface layer. Since electrophysiological recording methods rely heavily on electrode-cell proximity, this layer significantly attenuates the signal amplitude making the use of traditional planar electrodes unsuitable. To penetrate into the tissue, bypassing the tissue surface, and to record and stimulate neural activity in the healthy interior volume of the slice, an array of 61 micro-needles was fabricated.
  
  
  RESULTS
  This device is shown to record extracellular action potentials from individual neurons in acute cortical slices with a signal to noise ratio of up to ∼15:1. Electrical stimulation of individual neurons is achieved with stimulation thresholds of 1.1-2.9 µA.
  
  
  CONCLUSIONS
  The novelty of this system is the combination of close needle spacing (60 µm), needle heights of up to 250 µm and small (5-10 µm diameter) electrodes allowing the recording of single unit activity. The array is coupled to a custom-designed readout system forming a powerful electrophysiological tool that permits two-way electrode-cell communication with populations of neurons in acute brain slices.
authors.affiliation: IOP, University of Strathclyde, Glasgow G4 0NW, UK. deborah.gunning@strath.ac.uk
authors.forename: D E
authors.initials: DE
authors.lastname: Gunning
authors.forename: J M
authors.initials: JM
authors.lastname: Beggs
authors.forename: W
authors.initials: W
authors.lastname: Dabrowski
authors.forename: P
authors.initials: P
authors.lastname: Hottowy
authors.forename: C J
authors.initials: CJ
authors.lastname: Kenney
authors.forename: A
authors.initials: A
authors.lastname: Sher
authors.forename: A M
authors.initials: AM
authors.lastname: Litke
authors.forename: K
authors.initials: K
authors.lastname: Mathieson
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001921:Brain / Q000502:physiology*; D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods; D017736:Ion-Selective Electrodes; D008839:Microelectrodes; D009339:Needles / Q000600:supply & distribution*; D009415:Nerve Net / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D009924:Organ Culture Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley