title: Histological assessment of thermal damage in the brain following infrared neural stimulation.
abstract: BACKGROUND
  Infrared neural stimulation (INS) is a novel technique for modulating neural function. Its advantages over electrical stimulation include high spatial specificity, lack of electrical artifact and contact-free stimulation. INS acts via a rapid, focal increase in temperature. However, in order to become a viable experimental and therapeutic tool, the safety of INS must be demonstrated.
  
  
  OBJECTIVE
  Our aim was to determine the upper limit for the radiant exposure of INS in the brain without causing damage, using an INS sequence previously shown to induce both behavioral and electrophysiological effects in rodents and non-human primates.
  
  
  METHODS
  We stimulated the brains of anesthetized rodents and two squirrel monkeys using an infrared laser, depositing radiant energies from 0.3 to 0.9 J/cm2 per pulse in 0.5 s-long 200 Hz trains. At the end of the experiment, the animals were euthanized, perfused and the brains processed using standard histological techniques.
  
  
  RESULTS
  Radiant exposures greater than or equal to 0.4 J/cm2 resulted in identifiable lesions in brain sections. The lesions had a shape of a parabola and could further be subdivided into three concentric zones based on the type of damage observed.
  
  
  CONCLUSIONS
  The thermal damage threshold following our INS paradigm was between 0.3 and 0.4 J/cm2 per pulse. This value is lower than the one found previously in peripheral nerve. The differences are likely due to the structure of the INS sequence itself, particularly the repetition rate. The results warrant further modeling and experimental work in order to delimit the INS parameter space that is both safe and effective.
authors: Department of Psychology, Vanderbilt University, 111 21st Ave. South, 301 Wilson Hall, Nashville, TN 37240, USA. Electronic address: Mykyta.M.Chernov@Vanderbilt.edu.
authors: Mykyta Mikhailovich
authors: MM
authors: Chernov
authors: Department of Psychology, Vanderbilt University, 111 21st Ave. South, 301 Wilson Hall, Nashville, TN 37240, USA.
authors: Gang
authors: G
authors: Chen
authors: Department of Psychology, Vanderbilt University, 111 21st Ave. South, 301 Wilson Hall, Nashville, TN 37240, USA.
authors: Anna Wang
authors: AW
authors: Roe
mesh_terms: D000818:Animals; D001921:Brain / Q000473:pathology*; D001931:Brain Mapping / Q000379:methods; D004558:Electric Stimulation / Q000009:adverse effects* / Q000379:methods*; D004599:Electric Stimulation Therapy / Q000009:adverse effects* / Q000379:methods*; D007259:Infrared Rays / Q000009:adverse effects*; D010525:Peripheral Nerves / Q000473:pathology*; D051381:Rats; D012453:Saimiri; D013696:Temperature
keywords: Infrared neural stimulation; Non-human primate; Thermal damage