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1

A comparison of methods for analysis of temporal frequency tuning in visual responses

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Wierzbicka A., Kordecka K., Zygierewicz J., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
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2017
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tom 77
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nr Suppl.1
INTRODUCTION: There are numerous methods to study neuronal processing of information about temporal frequency content of visual stimuli. The two most fundamental methods are 1) direct measurement of response amplitude, e.g. an amplitude of averaged visual evoked potential, and 2) assessment of response magnitude after transformation of electrophysiological signal from time to frequency domain. AIM(S): The aim of this study was to find an appropriate analysis method to characterize cortical responses to visual stimuli of various temporal frequencies. METHOD(S): Visual responses were recorded from both primary visual cortices, contra- and ipsilateral to the stimulated eye, using multichannel linear electrode arrays during electrophysiology experiments performed on anesthetized rats. As a visual stimulus we used 2-ms-long LED flashes delivered at two frequencies: 1 and 7 Hz. RESULTS: We found that for frequency of 1 Hz it is difficult to draw conclusions based on power spectrum alone. For frequency of 7 Hz the assessment of evoked potential in time domain was highly inaccurate. CONCLUSIONS: For 1 Hz the estimation of the visual evoked potential amplitude by direct measurement should be also performed. For 7 Hz the analysis should be performed after transformation of the signal from the time to frequency domain. Our results also indicate the advantages of the Welch method in comparison to the periodogram to analyze signals in the frequency domain. FINANCIAL SUPPORT: Supported by the Polish National Science Center grant Symfonia 1 (2013/08/W/NZ4/00691).
2

Orientation tuning in mouse primary visual cortex – Intrinsic signal optical imaging study

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Raciborska I., Kordecka K., Posluszny A., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
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2017
|
tom 77
|
nr Suppl.1
INTRODUCTION: Accumulating body of research has shown a cardinal bias for preference of spatially oriented targets in different species including humans, indicating greater neuronal responses in the primary visual cortex for horizontal or vertical contours in opposite to oblique ones. AIM(S): We used intrinsic signal optical imaging, a popular tool to map cortical function in rodents to verify the hypothesis whether a cardinal bias is present also in mouse primary visual cortex. METHOD(S): The experiments were performed on 7 week old wild mice under isoflurane anaesthesia. Intrinsic signals were recorded using CCD camera set above the visual cortex. Visual stimuli, square-wave black-and-white gratings (spatial frequency 0.05 cycle/degree, and temporal frequency 2 Hz, four orientations: 0, 45, 90, 135 degree) drifting in two directions, back and forth, were presented in random order with uniform grey images in 16 trials. Imaging was performed under the control of Imager 3001 system. Data were collected with 10 Hz resolution from 1 s before stimulus onset, during 7 s of visual stimulation and to 1 s after stimulus offset with 7 s interval between recordings. RESULTS: Using the described protocol of visual stimulation and data collection we could successfully map cortical responses to visual stimuli of different orientations. Collected images showed the strongest responses for horizontally and vertically oriented gratings. CONCLUSIONS: Our results support the hypothesis of the bias toward cardinal orientation preference in mouse visual cortex. FINANCIAL SUPPORT: Supported by the Polish National Science Center grant Symfonia 1 (2013/08/W/ NZ4/00691).
3

Effect of temporary inactivation of rat visual cortex on visual responses in the superior colliculus

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Kordecka K., Foik A., Wierzbicka A., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
|
2017
|
tom 77
|
nr Suppl.1
INTRODUCTION: It is generally accepted that neuronal plasticity can be induced at the cortical level. In our previous study we observed that relatively strong visual stimulation enhanced responses both at the cortical and subcortical level. The backward projection from the visual cortex to superior colliculus (SC) may facilitate the reinforcement of response in this midbrain structure. AIM(S): In the current study we examined how inactivation of the visual cortex affects responses in the SC after visual training. METHOD(S): Visual evoked potentials (VEPs) were recorded in anesthetized rats (n=5) from the primary visual cortex (VCx) and the SC, contralateral to stimulated eye, in response to flashing white‑light‑emitting diodes (LEDs) placed 10 cm in front of the rat. Monocular visual stimulation consisted of series of 300 repetitions of light flashes with 2 s intervals, presented every 15 minutes through 3 hours. In order to temporary block the activity of the cortex after 3-hour visual stimulation, a well above the contralateral VCx was fulfilled with xylocaine solution (2.5%). During cortical inactivation a single series of visual stimulation (300 stimulus repetitions) was presented and the SC VEP amplitudes were analysed. RESULTS: Chemical inactivation resulted in strong attenuation of cortical VEP amplitudes. In the case of the SC, cortical deactivation did not cause any significant difference in VEP amplitudes as compared to responses after 3 h of visual training. Collicular VEPs were still at the high level and significantly differed from control recording at the beginning of training, which indicates a minor impact of the VCx on response enhancement in the SC. CONCLUSIONS: Temporary deactivation of the visual cortex didn’t result in decline of VEP amplitudes in the SC, which indicates that increase of responses in SC after visual training is most likely due to enhancement of the retinal input to the SC. FINANCIAL SUPPORT: Supported by the Polish National Science Center grant Symfonia 1 (2013/08/W/NZ4/00691).
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