M Pathway and Areas 44 and 45 Are Involved in Stereoscopic Recognition Based on Binocular Disparity

Japanese Journal of Physiology, 52, 191–198, 2002 M Pathway and Areas 44 and 45 Are Involved in Stereoscopic Recognition Based on Binocular Disparity Tsuneo NEGAWA, Shinji MIZUNO*, Tomoya HAHASHI, Hiromi KUWATA†, Mihoko TOMIDA, Hiroaki HOSHI*, Seiichi ERA, and Kazuo KUWATA Departments of Physiology, * Radiology, and † Nursing Course, Gifu University School of Medicine, Gifu, 500–8705 Japan Abstract: We characterized the visual path- was reported that these regions were inactive ways involved in the stereoscopic recognition of during the monocular stereopsis. To separate the the random dot stereogram based on the binocu- specific responses directly caused by the stereo- lar disparity employing a functional magnetic res- scopic recognition process from the nonspecific onance imaging (fMRI). The V2, V3, V4, V5, in- ones caused by the memory load or the inten- traparietal sulcus (IPS) and the superior temporal tion, we designed a novel frequency labeled sulcus (STS) were significantly activated during tasks (FLT) sequence. The functional MRI using the binocular stereopsis, but the inferotemporal the FLT indicated that the activation of areas 44 gyrus (ITG) was not activated. Thus a human M and 45 is correlated with the stereoscopic recog- pathway may be part of a network involved in the nition based on the binocular disparity but not stereoscopic processing based on the binocular with the intention artifacts, suggesting that areas disparity. It is intriguing that areas 44 (Broca’s 44 and 45 play an essential role in the binocular area) and 45 in the left hemisphere were also ac- disparity. [Japanese Journal of Physiology, 52, tive during the binocular stereopsis. However, it 191–198, 2002] Key words: stereoscopic recognition, binocular disparity, functional MRI, M pathway, frequency labeled task sequence. Environmental information is generally sent through Lesion analyses in humans [9–11] indicate that the several pathways that are parallel to the physically parietal cortex plays a major role with a suggestion of separated areas of the cerebral cortex, communicating right-hemisphere dominance for stereoscopic recogni- with one another to produce the integration. A stereo- tion. For example, patients with anterior temporal- scopic recognition is a typical example of the integra- lobe lesions demonstrate impaired global stereopsis tion of two-dimensional (2D) images of a three-di- but intact local stereoacuity [9]. Patients with right- mensional (3D) object projected in slightly different sided temporal lobe lesions perform significantly planes into a single-image having a 3D effect. Stereo- worse than those with left-sided lesions in perceiving scopic vision has been studied intensively at both the depth when it is cued by ambiguous disparities [10]. theoretical and computational levels [1–3]. Since Right hemisphere superiority has been suggested from stereoscopic recognition is known to exhibit a diverse works with normal human subjects [11]. Binocularly and moderately complicated phenomena, which are driven V3 complex cells project to the parieto-occipi- well suited for study at the neurophysiological level, tal area of the superior parietal lobule and lateral and human brain mapping involved in stereoscopic recog- posterior intraparietal areas in the lateral bank and nition have been of growing interest [4–8]. fundus of the intraparietal sulcus in the cat [12] and Received on June 28, 2001; accepted on February 6, 2002 Correspondence should be addressed to: Kazuo Kuwata, Department of Physiology, Gifu University School of Medicine, 40 Tsukasa- machi, Gifu, 500–8705 Japan. Tel: 181–58–267–2227, Fax: 181–58–267–2962, E-mail: [email protected] Japanese Journal of Physiology Vol. 52, No. 2, 2002 191 T. NEGAWA et al. the macaque monkey [13]. These cortical areas are tem equipped with a superconductive magnet operat- thought to be involved in the coding of spatial posi- ing at 1.5 T was used to perform MRI studies. Thir- tion or stereopsis, or both. However, the data on the teen consenting normal male volunteers participated. localization of this function in humans are still less All subjects were able to interconvert between 3D and specific, and the relationships with the established vi- 2D within 1 s. They were right-handed adult native sual pathways [14] have not yet been reported. Here, Japanese males 30–45 years old. Their dextral ability we first reported the human brain regions activated was confirmed by the Edinburgh inventory [19]. during stereopsy of the random dot stereogram [15] The paradigm used involved one 3D image (depth) and characterized the dominant visual pathways [14], and one 2D image (form), using two categories of using statistical parametric mapping (SPM) (Well- stimuli. The subjects wore a blue filter over the left come Department of Cognitive Neurology, Institute of eye and a red one over the right during the experi- Neurology, UCL, UK) of functional magnetic reso- ment. In the 3D condition, a colored random dot stere- nance imaging (fMRI). ogram (Fig. 1a) depicting a square at 100% binocular One of the important methodological difficulties is correlation was presented on the screen through a the separation of the specific responses from the unex- computer-controlled projector, MX-PJ1 (Minolta, pected nonspecific ones triggered by the tasks, possi- Osaka, Japan), using a software Visual Basic (Mi- bly unconsciously, such as those caused by the mem- crosoft, Washington, USA). The subjects could see ory load [16] or the intention itself [17]. To overcome only monochrome random dots even for a colored ran- this, we firstly designed the task sequence termed fre- dom dot stereogram because of filters. On the other quency labeled tasks (FLT) (see MATERIALS AND hand, in 2D condition, monochrome random dots with METHODS); thereby we can separate the task-specific the square frame (Fig. 1b) were presented. The sub- responses from the nonspecific ones. The main idea is jects viewed a screen on which the 3D and 2D images the labeling of the task-specific brain responses by were presented alternatively. Each session consisted of task-specific frequencies, which are incorporated into multiple 30-s epochs in a boxcar configuration. the task sequence, in analogy with the multidimen- A gradient echo planar imaging (EPI) sequence was sional heteronuclear NMR pulse sequence [18], where used on a Horizon 1.5 MRI system with the following each signal is labeled by the nuclear-specific reso- acquisition parameters: flip angle, 90°; field of view, nance frequencies. 320 mm3320 mm; matrix, 1283128 pixels with 14 In FLT, task is labeled by the specific frequency, slices; slice thickness, 8 mm; interslice gap, 3 mm; and brain responses caused by the task are detected by repetition time, 3 s. The spatial resolution was approx- using the correlation with the same frequency. On the imately 2.5 mm32.5 mm311 mm. Four hundred and other hand, nonspecific responses are not specifically twenty images were acquired during 90 s. The ses- correlated with any task-specific frequency. This is sions that showed brain motion exceeding 0.6 mm one of the novel aspects of this report. FLT may es- were performed again to avoid so-called fictitious ac- sentially distinguish brain regions activated by the tivation resulting from pixel misalignment. The fMRI stereoscopic recognition and those activated by the ar- time series data consisting of consecutive echo-planar tifacts. images for each slice were analyzed by the use of the SPM96 method on software MEDx Ver. 3.3 (Sensor MATERIALS AND METHODS Systems Inc., Virginia, USA). To increase S/N ratio, the data were smoothed with A Signa (GE Medical System, Horizon) imaging sys- a 535311 mm full-width-at-half-maximum Gaussian Fig. 1. Random dot stereogram uti- lized for the fMRI experiment. The subjects wore a blue filter over the left eye and a red one over the right eye during the experiment. The images were presented on the screen through a computer controlled projector, MX-PJ1 (Minolta), by the use of a software Visual Basic (Mi- crosoft). (a) Colored random dot stereogram. (b) Monochrome random dots with the square frame. 192 Japanese Journal of Physiology Vol. 52, No. 2, 2002 Functional MRI of Stereopsy kernel, and a high-pass filter and proportional global normalization (mean: 100) were applied. A statistical analysis was performed by using a delayed (6 s) boxcar model function in the context of the general linear model used in SPM96. Specific effects were tested by applying appropriate linear contrasts to the parameter estimates for each condition, resulting in a t-statistic for each voxel. Here the t-statistics, which were trans- formed to Z scores, constitute an activation map. These images were interpreted by referring to the probabilistic behavior of a Gaussian field. Functional MRI results were presented with contrast between two sets of images described earlier and showed activated areas that conformed to the statistical criteria of sig- nificance (p,0.05, corrected by multiple compari- son). The subtractive nature of the process effectively eliminated the activation areas common to the two types of visual stimuli, such as the primary visual cortex. Reproducibility of the analyzed data was confirmed individually for each subject. The anatomic identification of activated areas was performed individually by mapping these areas onto the subject’s own anatomic Fig. 2. General block diagrams of the frequency-la- T1-weighted images obtained with identical coordi- beled task sequences and correlation analyses. (a) Dia- nates. After identification of the neuroanatomic site of gram of TASK A (stereoscopic recognition based on binoc- the areas of activation performed individually for each ular disparity). (b) Diagram of TASK B (left-finger opposi- tion). (c) Correlation I for the detection of activated regions subject, the activated areas from all eight subjects by TASK A. (d) Correlation II for the detection of activated were calculated by a random effect model and mapped regions by TASK B.

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