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상구 안구운동신호의 신경 생리적 연구
Reports NRF is supported by Research Projects( 상구 안구운동신호의 신경 생리적 연구 | 2004 Year 신청요강 다운로드 PDF다운로드 | 이춘길(서울대학교) ) data is submitted to the NRF Project Results
Researcher who has been awarded a research grant by Humanities and Social Studies Support Program of NRF has to submit an end product within 6 months(* depend on the form of business)
사업별 신청요강보기
  • Researchers have entered the information directly to the NRF of Korea research support system
Project Number H00046
Year(selected) 2004 Year
the present condition of Project 종료
State of proposition 재단승인
Completion Date 2007년 05월 19일
Year type 결과보고
Year(final report) 2007년
Research Summary
  • Korean
  • 본 과제는 고양이 상구의 신경생리학적 연구와 인간의 공간 기억의 역동적 조절에 관한 정신물리적 연구의 두 부분으로 이루어졌다. 두 부분은 모두 공간시각과 행동을 이해하고자 한 것이었다.

    1. 고양이 상구의 신경생리적 연구
    상구는 도약안구운동을 제어하는 핵심적 뇌간 구조로 알려져 있다. 상구 세포들은, 망막과 시각피질 영역들로부터 공간 정보를 입력받아 이를 처리하여 안구와 머리 운동의 신호를 생성한다. 이전 연구에 의하면 운동에 관련된 변수들이 상구의 세포집단의 활동으로 표현되며, 세포활동의 시간 부호가 일정한 역할을 하는 것으로 알려져 있다. 본 연구에서는 훈련된 고양이가 시각자극을 향해서 안구운동을 하는 과제를 수행하는 동안에 고양이 상구의 활동을 여러 채널의 전극을 통해서 단일신경세포의 활동을 채집하여 시각, 운동 관련 활동의 동기화 변화를 분석하였다. 세포 활동의 주파수 분석, 시행간, 채널간 활동시간일치성을 분석하였는데, 이 결과 상구의 세포들은 시각자극에 대해서 주기적, 동기화된 활동을 보이며, 이 주기적 동기성은 시행간, 채널간 일치성을 보이고, 안구운동의 발생 시점에 가까워질수록 이러한 성질이 소멸하는 것을 발견하였다.

    2. 공간적 단기기억의 역동절 조절
    시각자극의 공간적 위치를 표상하는 것은 시각처리에서 핵심적인 과정인데, 자극의 위치에 관한 기억은, 응시 등의 내재적 과정, 혹은 자극과 동시에 존재하는 외재적 과정 등과 상호 작용하여 역동적으로 조절(왜곡)되는 것이 알려져 있다. 본 연구에서는 실험참가자(인간)가 다른 외부자극이 없는 상황에서 반응자극을 움직여서, 기억하고 있는 시각자극의 위치를 보고하는 과제를 수행하면서 보이는 위치 보고의 왜곡을 통해서, 자극의 위치 기억이 응시와 어떠한 상호작용을 하는지를 연구하였다. 10개의 관련된 실험을 통해서 얻어진 결과는, 시각표적의 위치 기억은 응시점으로부터, 또, 반응자극의 위치로부터 밀쳐진다는 가설의 예상과 가장 가까웠다. 따라서, 표적자극의 위치가 응시점과 반응자극 사이에 있을 때에는 표적자극의 위치에 관한 기억이 응시점과 반응자극으로부터 동시에 밀쳐져서 정확한 반면에, 반응자극의 위치가 응시점과 표적자극의 위치 가운데 있을 때에는 밀침이 합해져서 표적자극의 위치 기억이 외곽으로 왜곡되었다. 비슷한 왜곡 결과가 여러 실험 조건에서 반복적으로 관찰되었다. 표적자극과 반응자극의 거리가 가까울수록 밀침은 컸으며, 응시점으로부터의 밀침은 배경의 밝기에 따라 변함을 관찰하였다. 이 결과들은 시각 표적의 공간적 위치 기억이 응시점과, 외부 자극에 의해서 체계적으로 조절되는 현상을 확인하고 자극의 위치 보고의 왜곡에 관한 연구의 이전의 불일치하는 결과를 해석하는데 도움이 될 것이다.



  • English
  • This project consisted of two parts: neurophysiological study of the cat superior colliculus and dynamic modulation of spatial memory in human. Both projects aim to understand spatial vision and behavior.

    1. neurophysiological study of the cat superior colliculus
    The superior colliculus (SC) is an integrative brain stem structure that is critically involved in controlling the saccadic eye movements. The SC integrates visual inputs from the retina and cortical areas containing spatial information and generates motor command signals for eye and head movements. It has been known that the parameters of movements are encoded by the active neuronal population. It has been suggested that the temporal code takes parts in population coding by representing information contents or by modulating the signal transmission. We investigated the properties and temporal modulation of synchronized oscillatory discharge of the cat SC in relation to the generation of saccadic eye movements. Single-unit extracellular activity was recorded with multi-channel electrodes from the superior colliculus while the cat was performing a visually-guided saccade task. Results of analyses on the power spectrum, wavelet spectrum, inter-trial coherence, and inter-channel coherence indicated that the spike activity of the cat SC during a visually-guided saccade showed a rhythmic oscillation dominant at alpha range and the rhythm was coherent across trials and neurons, and that the rhythm was induced by the visual stimulus, not by saccadic eye movement or other events.

    2. Dynamic modulation of spatial short-term memory
    Representing the spatial location of a visual target is fundamental to central visual processing, but studies have shown that interactions with intrinsic processes, such as gaze fixation or shifts, and extrinsic events, such as simultaneously-present visual stimuli in the scene, easily distort spatial memory. Using an egocentric localization paradigm in which subjects moved a visual probe to report the remembered location of a visual target presented briefly on a wide screen during fixation, we found that the pattern of mislocalization was consistent with the hypothesis that the perceived target location is repulsed from both the probe and fixation loci. Thus, depending on spatial arrangement, the repulsions from the fixation and probe accumulated to result in a larger localization error, or the two repulsions annihilated each other to result in a veridical localization. Similar patterns of mislocalization were robustly obtained under a range of experimental conditions, but with varying degrees of repulsions from the fixation and probe. Ashorter spatial distance between the target and probe was associated with a stronger repulsion, and repulsion from the fixation in the dark diminished on a computer monitor with additional external references. As the availability of the external frame of spatial reference increased on a computer monitor, the repulsions from both the fixation andprobe decreased, resulting in a drastically different pattern of mislocalization: an increase in localization accuracy and a localization bias toward the fixation locus. Thus, the combination of variable interactions between the target repesentation and fixation and between the target memory and probe may explain the various patterns of apparent mislocalization.


Research result report
  • Abstract
  • This project consisted of two parts: neurophysiological study of the cat superior colliculus and dynamic modulation of spatial memory in human. Both projects aim to understand spatial vision and behavior.

    1. neurophysiological study of the cat superior colliculus
    The superior colliculus (SC) is an integrative brain stem structure that is critically involved in controlling the saccadic eye movements. Neuronal inputs from retina, and other cortical areas containing spatial information are integrated and transformed into the motor related signals in the SC. The SC neurons consist a broadly-tuned topographic map. It has been known that many cells participates in this translation process simultaneously and the average vector of graded discharges in the active population determines the amplitude and direction of saccadic eye movements. This coding strategy that the brain encodes information by populations of cells rather than by single cells is called population coding. It has been suggested that the temporal code takes parts in population coding by representing information contents or by modulating the signal transmission. The evidences were found in various brain area where the temporal correlation of neural activity possibly participates in information representation. In addition, the neural synchrony also has been understood as a modulation mechanism of signal transmission and information processing. We investigated the properties and temporal modulation of synchronized oscillatory discharge in relation to the generation of saccadic eye movements. Single-unit extracellular activity was recorded with multi-channel electrodes from the superior colliculus while the cat performing a visually-guided saccade task. The concerted activity was quantified in two ways: spike synchrony and coherence of rhythmic oscillation.


    2. Dynamic modulation of spatial short-term memory

    Representing the spatial location of a visual target is fundamental to central visual processing, but studies have shown that interactions with intrinsic processes, such as gaze fixation or shifts, and extrinsic events, such as simultaneously-present visual stimuli in the scene, easily distort spatial memory. Using an egocentric localization paradigm in which subjects moved a visual probe to report the remembered location of a visual target presented briefly on a wide screen during fixation, we found that the patternof mislocalization was consistent with the hypothesis that the perceived target location is repulsed from both the probe and fixation loci. Thus, depending on spatial arrangement, the repulsions from the fixation and probe accumulated to result in a larger localization error, or the two repulsions annihilated each other to result in a veridical localization. Similar patterns of mislocalization were robustly obtained under a range of experimental conditions, but with varying degrees of repulsions from the fixation and probe. Ashorter spatial distance between the target and probe was associated with a stronger repulsion, and repulsion from the fixation in the dark diminished on a computer monitor with additional external references. As the availability of the external frame of spatial reference increased on a computer monitor, the repulsions from both the fixation andprobe decreased, resulting in a drastically different pattern of mislocalization: an increase in localization accuracy and a localization bias toward the fixation locus. Thus, the combination of variable interactions between the target repesentation and fixation and between the target memory and probe may explain the various patterns of apparent mislocalization.

  • Research result and Utilization method
  • 1. neurophysiological study of the cat superior colliculus
    Eye position and extracellular single unit activity were recorded while the animals were performing a visually-guided saccade task. Single spikes with their waveforms were extracted off-line from the extracellular potentials above a certain threshold. Spike trains of the cells from 45 channels were wavelet transformed. Wavelets from one to eighty hertz with 1ms time index were convoluted with every spike train of every trial. Dominant frequency ranged between 11-20Hz (12 Hz on average) and the amplitude reached the peak at 87.68ms. The rhythm remained significant for 149.19ms. Alpha and beta frequency were dominant after the target onset, and alpha was dominant before saccade onset and offset. The rhythm appeared with the visual response, reached the peak approximately 90ms after the target onset, remained significant for sometime, and then faded away. In order to verify that the rhythm had been visually induced, the inter-trial coherence (ITC) was calculated from the wavelet transformed data. The peak magnitude of ITC ranged in alpha band (9.59 ± 2.31 Hz), and it was concluded that the dominant rhythm was visually induced. In order to investigate whether, and how much, the cells in distant population oscillates together, ICC (inter-channel coherence) was calculated. Overall, the ICCs at the low frequency band were significant. Consistent to previous results, ICC reached the peak magnitude 69.48±22.10ms after target onset. According to the power spectrum, wavelet spectrum, ITC, and ICC, the frequency of the rhythmic oscillation was dominant at alpha range. In addition, it could be concluded that the rhythm was induced by visual stimulus, not by saccadic eye movement or other events.

    2. Dynamic modulation of spatial short-term memory
    Spatial location of a visual target can be registered with respect to concurrent visual references, or with respect to the observer. When a visual reference is not available, e.g. in the dark, spatial localization depends on only egocentric cues, and its accuracy is often compromised. When a visual probe was used to report the remembered location of the target, the accuracy of the target localization depended on the initial position of the probe. When the probe initially appeared on the same side as the fixation with respect to the target (SS condition), the remembered target location was systematically biased beyond the target eccentricity. On the other hand, in the OS trials where the probe initially appeared on the side opposite to the fixation with respect to the target, localization was relatively accurate. The difference in localization bias between the SS and OS conditions persisted regardless of the gaze direction during the response period or the response device tested. Also, this difference persisted, although modulated, when the temporal gap between the fixation target offset and target onset was increased to 1s or when the temporal gap between the target offset and probe onset was increased to 1.2s. We also found this difference in the presence of a persistent external reference at the initial fixation. The asymmetric pattern of mislocalization between the OS and SS conditions is the closest to the prediction made by the hypothesis that the target memory is repulsed from both the fixation and the probe. Thus, repulsion from the fixation and probe either annihilate to result in near veridical localization in the OS condition, or accumulate to result in a larger localization error in the SS condition. The relatively accurate localization in the OS trials suggests that repulsions from the fixation and probe are comparable in magnitude. Under our experimental condition, the fixation and probe repulsed the target memory approximately by 0.15 and 0.18 deg, respectively, for each degree of target eccentricity.
  • Index terms
  • superior colliculus, spatial vision, spatial memory, psychophysics, neurophysiology, cat, human, single-cell recording, temporal coding, coherence, phase analysis, saccadic eye movement
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