1. Auditory monitoring for preservation of the function of the auditory nerve Recording of auditory evoked potentials in operations in the posterior fossa

2. Different conventions for display of ABR

3. NEURAL GENERATORS OF ABR:

4. Peak I: distal auditory nerve Peak II: central auditory nerve Peak III: mainly cochlear nucleus Peak IV: unknown Peak V: termination of the lateral lemniscus in the contralateral inferior colliculus

5. Intraoperative monitoring of auditory evoked potentials Interpretable response must be obtained in the shortest possible time Techniques are different from clinical use of ABR

6. Recording parameters for obtaining an interpretable responses in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

7. Recording parameters for obtaining an interpretable responses in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

8. Effect of stimulus rate on amplitude of ABR

9. Gain from increasing the stimulus rate

10. Recording parameters for obtaining an interpretable responses in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

11. Earphones

13. Recording parameters for obtaining an interpretable responses in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

14. Auditory brainstem evoked potentials (ABR): The latencies of the peaks are important therefore: Enhance the peaks by using optimal filtering

15. Digital filtering can enhance the waveform of the ABR

16. Recording parameters for obtaining an interpretable responses in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

17. Dipoles of ABR

18. Recording parameters for obtaining an interpretable ABR in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

19. Find the source of interference

20. Recording directly from the auditory nerve Provides nearly instantaneous monitoring of neural conduction in the auditory nerve

21. Cotton wick recording electrode

24. ABR: Vertex-neck Earlobe- earlobe Auditory nerve:

25. ABR Vertex-neck Unfiltered Filtered CAP from CNVIII Distally Near brainstem

26. Normal CAP Injury from heat Response from auditory nerve

27. Before surgical manipulations Solid lines: Rarefaction clicks Dashed lines: Condensation clicks After surgical manipulations

28. Waveform of the CAP recorded from the exposed CNVIII depends on pre-existing hearing loss

29. The recording electrode is difficult to keep in place on the CNVIII Recording from the surface of the cochlear nucleus

30. Recording from the cochlear nucleus: Recording electrode is placed in the lateral recess of the fourth ventricle

31. TUMOR CN VIII FLOCCULUS FORAMEN OF LUSCHKA WICK ELECTRODE ELECTRODE WIRE UNDER DURA SUTURES CN IX & CN X ELECTRODE WIRE CHOROID PLEXUS FROM: MOLLER ET AL 1994

32. Auditory nerve injuries affect speech discrimination more than cochlear injuries