Activity of a PTN from the forelimb representation during different postural tests A, control. B, standing on two forelimbs. C, standing on two hindlimbs. D, antiphase tilts of the F and H platforms. E, standing BIX 02189 on the right forelimb. F, standing on the left forelimb. For each test there are shown: the phase histogram of spike activity in the tilt cycle, the 1st harmonic of Fourier image, the mean frequency of discharge, and the preferred phase. preferred phase was similar to that in control. However, when only the left forelimb was standing on the platform the response was small and the neuron was slightly more active in the second half of the cycle. From Fig. 3 one can also see that the mean frequency of the neuron in most of the tests was similar.
The results illustrated in Fig. 3 demonstrated that this particular PTN received its main tilt related input Cilomilast from the contralateral forelimb, and additional very small inputs from the ipsilateral forelimb and from the hindlimbs. The phases of additional inputs differed considerably from that of the main input. One should note, however, that lifting of the limb strongly reduced tilt related movements of this limb but some small movements could still remain due to mechanical influences of the supporting limb. These residual limb movements could produce small rhythmical influences on PTNs of the lifted limb. Results shown forPTNno. 3566 in Fig. 3were typical for both fore and hindlimb PTNs: in the majority of them, the tilt related modulation was determined mainly by input from the contralateral fore or hindlimb, respectively.
These common features were reflected in the population characteristics of PTNs. Population characteristics of PTNs Three characteristics were used to describe postural responses in the forelimb and in the hindlimb PTN populations: The value of modulation, M1, the mean frequency in the tilt cycle, f 0 these values were averaged over the whole population of PTNs, and the distribution of preferred phases of response of forelimb or hindlimb PTNs over the tilt cycle. To evaluate the contribution of different limbs to the generation of PTN responses to tilts, we compared these three values across different tests. Figure 4. Population characteristics of forelimb PTN responses in tests revealing influences from shoulder and hip girdles A, mean value of modulation.
B D, algebraic differences between preferred phases of individual PTNs in tests 2F and 2F2H, in tests 2H and 2F2H, and in tests 2F2H/Anti and 2F2H. Influences from shoulder and hip girdles Forelimb PTNs. A contribution of postural mechanisms of an individual girdle to the periodical modulation of the forelimb PTNs was examined by lifting the hind or forequarters, as well as by tilting them in antiphase. Figure 4A shows that, when the cat stood on the forelimbs only, the response slightly increased as compared to control. By contrast, standing on only the hindlimbs led to a considerable decrease of the response. The values of responses in different tests are given in Table 1, together with the mean value of frequency in the tilt cycle. Lifting of the forequarters and lifting of the hindquarters produced also very different effects on the phases of PTN res