IV. ANÁLISIS E INTERPRETACIÓN DE RESULTADOS
4.4. RESULTADOS
Simultaneous recording in response to constant IHz stroboscopic illumination from two tectal locations for a period of up to 2 hours was achieved in 12 animals. In 6 of the animals the two receptive fields were non-overlapping in visual space and in the other 6 they were overlapping (Table 4.1). In all overlapping receptive fields the cross-correlations, at the beginning of stroboscopic illumination, revealed a large central peak indicating synchronised firing behaviour. After prolonged exposure to
stroboscopic illumination the number of events which occurred coincidently {ie at t =
0 seconds) increased indicating an improvement in the degree of correlation between the firing patterns recorded from these overlapping receptive fields (figure 4.6). Non overlapping receptive fields revealed a different behaviour pattern to prolonged
stroboscopic illumination. The CC at the start of stroboscopic entrainment was, in all cases, flat with no central peak but after longer periods of strobing a central peak at 0 seconds would appear (figure 4.7).
p - m
0 . 2
0 . 4
Figure 4.6. C ross-correlations calculated from overlapping receptive fields during l l l z stroboscopic illum ination.
E vent da ta w a s sim u lta n e o u sly recorded from o v e rla p p in g re cep tiv e fields. C ro s s -c o rre l a tio n s w e r e c a lc u la te d at 15 m in u te interv als (consecutive c o rr e le lo g ra m s fro m b o tto m to top) d u r in g constant e x p o s u r e to I H z stro b o sc o p ic il lum ination. T h e first graph w as o b ta in e d d u r i n g a 20 seco n d p eriod i m m e d i a te ly fo llo w in g the initial e x p o s u r e to stroboscopic il lu m in a tio n . T h e n u m b e r o t ev en ts
o c c u r r in g at a giv en ti m e is d epicted on the ordinate and the time at w h ic h th es e e v e n ts o c c u r is on the a b sc issa . A central peak is present in the first gra ph indicating c o rr e la tio n o f tiring p atterns
im m e d ia te ly on e x p o s u r e to the stro be. T h is peak gets larger w ith co n tin u e d e x p o s u r e to s t ro b o sc o p ic i l lu m in a tio n as d o o th e r peaks eith er side o f the central peak at 0 seco n d s . F o r e x a m p l e a peak at 4-0.2 s e c o n d s is clea rly v is ib le after 1 h o u r o f constant stroboscopic illu m in atio n . T h is im plies that an event a p p e a r s in o n e M U R F w h ic h is consistently 200m sec out o f phase w ith the e v e n ts in the seco n d M U R F . T h is st r o b o s c o p ic en tr a in m e n t effect was docu m en ted in the raster d is p la y s in figure 4 .2 . It is also ap p a r e n t fr om this se ries o f cro s s-c o rr e la tio n plots that the level o f b a c k g r o u n d gets g reater d u r in g e x p o s u r e to constant I H z stro b o sc o p ic illu m ination. T h is is c onsiste nt with the gradual increase in firing rate s h o w n in the rate plo ts in figure 4 .2 which w ere calc ulated fr om indix idual sustain ed , event and d i m m e r type M U R F s d u rin g I H z stroboscopic illu m in atio n.
ÉiÉÉiMU 4001
300
-200
1 0 0 ^ 0 J ÉÉHMÉIémUifyiTfirîiTf'fIrt'fi'i11111II111111111M s
-0 . 4
-0 . 2
0 . 0
0 . 2
0. 4
F i g u r e 4 . 7 . C r o s s - c o r r e l a t i o n s c a l c u l a t e d f r o m n o n - o v e r l a p p i n g r e c e p t i \ e fields d u r i n g I H z s t r o b o s c o p i c i l l u m i n a t i o n .In this e x p e r im e n t event da ta w as sim ultaneously recorded fr om non- o \ e rla p p in g receptive fields. C r o s s - c o r r e l a t i o n s w ere calc ulated at 15 m inute intervals ( c o n s e c u tiv e c o r r e le l o g r a m s from b o t t o m to top) d u r i n g constant e x p o s u r e to I H z stroboscopic illu m in atio n . The first grajih w as obtained d u r i n g a 2 0 s e c o n d p e rio d im m ed iately follow ing the initial e x p o s u r e to s tro b o s c o p ic illu m in atio n. C o n v e n t i o n s a re the sa m e as figure 4 .6 . H o w ev er, no central pe<ik is present in the first c r o s s
c o r r e l a t io n w h ic h w a s calculated fr om the initial response to stro b o sc o p ic illu m in atio n . A fte r 1 h o u r o f c o n s ta n t s tr o b o s c o p i c illu m in atio n a central peak was observed in the c o r r e le l o g r a m s \ inptom atic o f c o r r e la t e d n e u r o n a l activity.
4.2.4. The chronic effects of stroboscopic illumination on the developing