Lee Jungah, Groh Jennifer M
Center for Cognitive Neuroscience, Department of Psychology and Neuroscience, Department of Neurobiology, Duke University, Durham, North Carolina, United States of America.
PLoS One. 2014 Jan 15;9(1):e85017. doi: 10.1371/journal.pone.0085017. eCollection 2014.
Maps are a mainstay of visual, somatosensory, and motor coding in many species. However, auditory maps of space have not been reported in the primate brain. Instead, recent studies have suggested that sound location may be encoded via broadly responsive neurons whose firing rates vary roughly proportionately with sound azimuth. Within frontal space, maps and such rate codes involve different response patterns at the level of individual neurons. Maps consist of neurons exhibiting circumscribed receptive fields, whereas rate codes involve open-ended response patterns that peak in the periphery. This coding format discrepancy therefore poses a potential problem for brain regions responsible for representing both visual and auditory information. Here, we investigated the coding of auditory space in the primate superior colliculus(SC), a structure known to contain visual and oculomotor maps for guiding saccades. We report that, for visual stimuli, neurons showed circumscribed receptive fields consistent with a map, but for auditory stimuli, they had open-ended response patterns consistent with a rate or level-of-activity code for location. The discrepant response patterns were not segregated into different neural populations but occurred in the same neurons. We show that a read-out algorithm in which the site and level of SC activity both contribute to the computation of stimulus location is successful at evaluating the discrepant visual and auditory codes, and can account for subtle but systematic differences in the accuracy of auditory compared to visual saccades. This suggests that a given population of neurons can use different codes to support appropriate multimodal behavior.
在许多物种中,地图是视觉、体感和运动编码的主要形式。然而,灵长类动物大脑中尚未有关于空间听觉地图的报道。相反,最近的研究表明,声音位置可能通过广泛响应的神经元进行编码,其放电率大致与声音方位成比例变化。在额叶空间内,地图和这种速率编码在单个神经元水平上涉及不同的反应模式。地图由表现出限定感受野的神经元组成,而速率编码涉及在外围达到峰值的开放式反应模式。因此,这种编码格式差异给负责表征视觉和听觉信息的脑区带来了潜在问题。在这里,我们研究了灵长类动物上丘(SC)中听觉空间的编码,上丘是一个已知包含用于引导扫视的视觉和动眼神经地图的结构。我们报告,对于视觉刺激,神经元表现出与地图一致的限定感受野,但对于听觉刺激,它们具有与位置的速率或活动水平编码一致的开放式反应模式。这些不同的反应模式并未分离到不同的神经群体中,而是出现在相同的神经元中。我们表明,一种读出算法,即SC活动的位点和水平都有助于刺激位置的计算,在评估不同的视觉和听觉编码方面是成功的,并且可以解释与视觉扫视相比听觉扫视准确性中的细微但系统的差异。这表明给定的神经元群体可以使用不同的编码来支持适当的多模态行为。