OTHER ELECTRODES 



advantage if the insulator is 'non-wettable', but if it is not, the insulator is 

 best coated with silicone. 



FIXATION OF ELECTRODES 



Where electrodes are to be left in place over days or weeks it is vital that 

 the exact position of the tip be known, and also that it should stay firmly 

 fixed in position. A poorly fixed electrode will not only give useless informa- 

 tion but may also destroy large areas of brain. 



Electrode fixed 

 in cement 



Socket, plastic or stainless steel 

 screwed into hole in skull 



Layer of dental cement holding 

 electrodes to socket 



Electrodes in position 



Drilled stainless steel screw 



Cement 



Figure 36.2 Fixation of electrodes in brain 



A simple technique for implanting electrodes in the brain of rabbits is 

 described by Harris^ and in cats by Bradley and Elkes^. The electrode, 

 either unipolar or bipolar, is made of suitable wire insulated with non- 

 irritant resin or glass. It is held in a stereotaxic instrument and inserted 

 into the brain through a hole drilled in the roof of the skull and an incision 

 through the dura mater. By using known co-ordinates for the particular 

 brain the electrode tip can be placed with considerable accuracy in any 

 desired position, which is then checked by radiograph before the electrode 

 is finally fixed. The electrode and hole in the skull are packed with dental 

 acrylic resin which hardens in a few minutes leaving the electrode firmly 

 held in the skull. The wire is then released from the clamp, any excess is 

 cut off and the top with its connecting lead is smoothed over with more 

 resin. The skin can be sutured over the top of the electrode base and the 

 leads taken subcutaneously to any desired point before they are brought 



572 



