Multimodal architectonic mapping of human superior temporal gyrus

Although it is generally accepted that human superior temporal gyrus is activated by a huge variety of auditory and linguistic tasks, little is known about the exact positions and extents of cortical areas that are located on the lateral convexity of the gyrus (e.g., Brodmann’s area 22). Such information, however, is relevant for a rigorous testing of structural-functional relationships in both normal volunteers and patients suffering from disorders of auditory and language perception. The present combined cytoarchitectonic and receptorarchitectonic study identifies a distinct area (Te3) in the lateral bulge of the superior temporal gyrus by using an algorithm-based approach for the detection of cortical borders. Our mapping data show that, in contrast to Brodmann’s area (BA) 22, only small portions of Te3 reach the dorsal and ventral banks of the gyrus. Therefore, we labelled the newly defined area as “Te3” and not as “BA 22”. The cytoarchitectonically defined borders of Te3 coincide with abrupt changes in the receptorarchitecture of several classical neurotransmitters, suggesting that Te3 represents a functionally relevant area of the human superior temporal gyrus. Since position and extent of area Te3 varied considerably between subjects, probability maps were created that show for each voxel of the standard references space, the frequency with which Te3 was present in it. These maps, in combination with previously published maps of the primary auditory cortex, can directly be compared with functional imaging data, and may open new perspectives for the analysis of structural-functional correlations in the human auditory and language systems.     

A stereological approach to human cortical architecture: identification and delineation of cortical areas

Stereology offers a variety of procedures to analyze quantitatively the regional and laminar organization in cytoarchitectonically defined areas of the human cerebral cortex. Conventional anatomical atlases are of little help in localizing specific cortical areas, since most of them are based on a single brain and use highly observer-dependent criteria for the delineation of cortical areas. In consequence, numerous cortical maps exist which greatly differ with respect to number, position, size and extent of cortical areas. We describe a novel algorithm-based procedure for the delineation of cortical areas, which exploits the automated estimation of volume densities of cortical cell bodies. Spatial sampling of the laminar pattern is performed with density profiles, followed by multivariate analysis of the profiles' shape, which locates the cytoarchitectonic borders between neighboring cortical areas at sites where the laminar pattern changes significantly. The borders are then mapped to a human brain atlas system comprising tools for three dimensional reconstruction, visualization and morphometric analysis. A sample of brains with labeled cortical areas is warped into the reference brain of the atlas system in order to generate a population map of the cortical areas, which describes the intersubject variability in spatial conformation of cortical areas. These population maps provide a novel tool for the interpretation of images obtained with functional imaging techniques.     

Topographical organization of the cortical afferent connections to the cortex of the anterior ectosylvian sulcus in the cat

Summary The cortical afferents to the cortex of the anterior ectosylvian sulcus (SEsA) were studied in the cat, using the retrograde axonal transport of horseradish peroxidase technique. Following injections of the enzyme in the cortex of both banks, fundus and both ends (postero-dorsal and anteroventral) of the anterior ectosylvian sulcus, retrograde labeling was found in: the primary, secondary, and tertiary somatosensory areas (SI, SII and SIII); the motor and premotor cortices; the primary, secondary, anterior and suprasylvian fringe auditory areas; the lateral suprasylvian (LS) area, area 20 and posterior suprasylvian visual area; the insular cortex and cortex of posterior half of the sulcus sylvius; in area 36 of the perirhinal cortex; and in the medial bank of the presylvian sulcus in the prefrontal cortex. Moreover, these connections are topographically organized. Considering the topographical distribution of the cortical afferents, three sectors may be distinguished in the cortex of the SEsA. 1) The cortex of the rostral two-thirds of the dorsal bank. This sector receives cortical projections from areas SI, SII and SIII, and from the motor cortex. It also receives projections from the anterolateral subdivision of LS, and area 36. 2) The cortex of the posterior third of the dorsal bank and of the posterodorsal end. It receives cortical afferents principally from the primary, secondary and anterior auditory areas, from SI, SII and fourth somatosensory area, from the anterolateral subdivision of LS, vestibular cortex and area 36. 3) The cortex of the ventral bank and fundus. This sulcal sector receives abundant connections from visual areas (LS, 20, posterior suprasylvian, 21 and 19), principally from the lateral posterior and dorsal subdivisions of LS. It also receives abundant connections from the granular insular cortex, caudal part of the cortex of the sylvian sulcus and suprasylvian fringe. Less abundant cortical afferents were found to arise in area 36, second auditory area and prefrontal cortex. The abundant sensory input of different modalities which appears to converge in the cortex of the anterior ectosylvian sulcus, and the consistent projection from this cortex to the deep layers of the superior colliculus, make this cortical region well suited to play a role in the control of the orientation movements of the eyes and head toward different sensory stimuli.Supported by FISSS grants 521/81 and 1250/84     

The neural origin generating early cortical components of SEP: Topographical analysis using temporal-second-order-differentiation of cortical SEPs

Summary In order to identify dipole generators of the N20/P20 and P25, we employed second-order-differentiation in the temporal dimension (temporal-second-order-differentiation; TSOD) with t=2 msec. The rate of variation in the voltage of cortical SEPs calculated by TSOD identified responses of each dipole, reflecting the density of neuronal firing. On topographic analysis, the distributions of N20/P20 and P25 conformed to the shape of gyrus better in the TSOD maps than in the isovoltage maps. The TSOD maps indicated that N20 and P25 were post-central components and that P20 was a pre-central one. Therefore, we concluded that the two dipoles generating N20/P20 and P25 were located in the posterior wall of the central sulcus (area 3b) and the crown (areas 1 and 2) of the post-central gyrus, respectively.     

Multimodal characterisation of cortical areas by multivariate analyses of receptor binding and connectivity data

Cortical areas are regarded as fundamental structural and functional units within the information processing networks of the brain. Their properties have been described extensively by cyto-, myelo- and chemo-architectonics, cortical and extracortical connectivity patterns, receptive field mapping, activation properties, lesion effects, and other structural and functional characteristics. Systematic integrative approaches aiming at multimodal characterisations of cortical areas or at the delineation of global features of the cortical network, however, are still scarce and usually limited to a single data modality, such as cytoarchitectonical or tract tracing data. Here we describe a methodological framework for the systematic evaluation, comparison and integration of different data modalities from the brain and demonstrate its practical application and significance in the analysis of receptor binding and connectivity data within the motor and visual cortices of macaque monkeys. The framework builds on algorithmic methods to convert data between different cortical parcellation schemes, as well as on statistical techniques for the exploration of multivariate data sets comprising data of different types and scales. Thereby, we establish a relationship between intrinsic area properties as expressed by quantitative receptor binding, and extrinsic inter-area communication, which relies on anatomical connectivity. Our analyses provide preliminary evidence for a good correspondence of these two data types in the motor cortex, and their partial discrepancy in the visual cortex, raising hypotheses about the different organisational aspects highlighted by receptors and connectivity. The methodological framework presented here is flexible enough to accommodate a wide range of further data modalities, and is specific enough to permit novel insights and predictions concerning brain organisation. Thus, this approach promises to be very useful in the endeavour to characterise multimodal structure-function relationships in the brain. Accepted: 9 May 2001     

Spatial representation of corticofugal input in the inferior colliculus: a multicontact silicon probe approach

The inferior colliculus (IC) is a well-established target of descending projections from the auditory cortex (AC). However, our understanding of these pathways has been limited by an incomplete picture of their functional influence within the three-dimensional space of the IC. Our goal was to study the properties and spatial representation of corticofugal input in the IC of guinea pigs with a high degree of spatial resolution. We systematically mapped neural activity in the IC using two types of silicon substrate probes that allow for simultaneous recording at multiple neural sites. One probe provided a high resolution in the dorsal-ventral plane and the other provided spatial resolution in the medial-lateral plane. Electrical stimulation of the ipsilateral AC produced excitatory responses in the IC with thresholds usually below 5–10 µA. First spike latencies were predominantly in the 6–20 ms range, although latencies from 3–5 ms were also observed. Broadly distributed unimodal spike patterns with modal latencies greater than 30 ms were occasionally seen. The excitatory responses to cortical stimulation were mostly unimodal and occasionally bimodal with a wide range of spike distribution patterns and response durations. Excitation was often followed by suppression of spontaneous activity. Suppression of acoustic responses was observed even when there was little or no response to electrical stimulation, suggesting spatial-temporal integration. A few of the responding neurons showed purely inhibitory responses to electrical stimulation, suggesting that there are disynaptic routes of corticocollicular inhibition. Detailed spatial mapping revealed that the response patterns and their durations had a characteristic spatial distribution in the IC.     

Parcellation of cortical areas by in situ hybridization for somatostatin mRNA in the adult rat: frontal, parietal, occipital, and temporal regions

The expression of somatostatin mRNA within the neocortex of the rat was examined by in situ hybridization with an alkaline phosphatase-labeled probe. We sought to determine whether parcellation of the neocortex could be based upon the number and laminar location of the hybridized cells. Our investigation demonstrated that the boundaries of the neocortical areas can be determined by the distribution pattern of neurons expressing somatostatin mRNA. Few hybridized cells were located within layer IV, and this sparsity of cells within their wide granular layer marked the primary sensory areas. The occipital region was stratified, with insensely labeled cells in layers II/III and VI and faintly labeled cells in layer V. The parietal region carried a similar stratification, but more space between intensely labeled cells in layers III and V and between layers V and VI gave the region a three-tiered appearance. The temporal region displayed intensely labeled cells dispersed throughout layers III and VI and many in layer V as well as those faintly labeled without any breaks between the laminae. The distribution of the cells hybridized for somatostatin mRNA formed two configurations within the frontal region. It was difficult to identify any lamination in the first area, whereas the second area demonstrated a stratification reminiscent of the parietal region, but with only two tiers. The conclusion of the investigation is that in situ hybridization for somatostatin mRNA provides an exceptional means by which the areal boundaries within the neocortex may be drawn.     

Flattened cortical maps of cerebral function in the rat: a region-of-interest approach to data sampling, analysis and display

We describe a method for the measurement, analysis and display of cerebral cortical data obtained from coronal brain sections of the adult rat. In this method, regions-of-interest (ROI) are selected in the cortical mantle in a semiautomated fashion using a radial grid overlay, spaced in 15 degrees intervals from the midline. ROI measurements of intensity are mapped on a flattened two-dimensional surface. Topographic maps of statistical significance at each ROI allow for the rapid viewing of group differences. Cortical z-scores are displayed with the boundaries of brain regions defined according to a standard atlas of the rat brain. This method and accompanying software implementation (Matlab, Labview) allow for compact data display in a variety of autoradiographic and histologic studies of the structure and function of the rat brain.     

Morphological classification and identification of neurons in the inferior colliculus: a multivariate analysis

In this paper a modern statistical method is applied to an old cell classification and identification problem in the central nucleus of the inferior colliculus. In a recent computer-based reconstruction study of Golgi-impregnated neurons in the rat, two types of cell with flattened dendritic arbors, flat (F) and less flat (LF), were defined. Both types contributed to the anisotropic and laminar pattern of the nucleus. The classification was based on five morphological features of complete dendritic arbors, two assessed visually and three numerically. With respect to the latter criteria, the two types were classified by preselected cut-off values. The distinction of the two types was supported, among other things, by a prevailing spatial segregation into laminar and interlaminar compartments. The cell sample was too small, however, to validate the classification and segregation definitively. In the present study, the classification is tested by the partial least squares regression method which is independent of the preselected cut-off values, and is able to handle small sample sizes and interdependent variables. In the plots, the F and LF cells are clearly separated into two distinct clusters, strongly supporting the distinction of the two types. The different density of the two clusters shows that the F cells are more homogeneous that the LF cells. The relative importance of the classification criteria is also evaluated. The three-dimensional (3D) inspection and the 3D convex hull-based form factor were found to be the most powerful criteria for identifying the two cell types, while the 2D evaluation of camera lucida drawings, a standard method in neuroanatomy, proved to have the least predictive value.     

Cytoarchitectonic mapping of the human amygdala, hippocampal region and entorhinal cortex: intersubject variability and probability maps

Probabilistic maps of neocortical areas and subcortical fiber tracts, warped to a common reference brain, have been published using microscopic architectonic parcellations in ten human postmortem brains. The maps have been successfully applied as topographical references for the anatomical localization of activations observed in functional imaging studies. Here, for the first time, we present stereotaxic, probabilistic maps of the hippocampus, the amygdala and the entorhinal cortex and some of their subdivisions. Cytoarchitectonic mapping was performed in serial, cell-body stained histological sections. The positions and the extent of cytoarchitectonically defined structures were traced in digitized histological sections, 3-D reconstructed and warped to the reference space of the MNI single subject brain using both linear and non-linear elastic tools of alignment. The probability maps and volumes of all structures were calculated. The precise localization of the borders of the mapped regions cannot be predicted consistently by macroanatomical landmarks. Many borders, e.g. between the subiculum and entorhinal cortex, subiculum and Cornu ammonis, and amygdala and hippocampus, do not match sulcal landmarks such as the bottom of a sulcus. Only microscopic observation enables the precise localization of the borders of these brain regions. The superposition of the cytoarchitectonic maps in the common spatial reference system shows a considerably lower degree of intersubject variability in size and position of the allocortical structures and nuclei than the previously delineated neocortical areas. For the first time, the present observations provide cytoarchitectonically verified maps of the human amygdala, hippocampus and entorhinal cortex, which take into account the stereotaxic position of the brain structures as well as intersubject variability. We believe that these maps are efficient tools for the precise microstructural localization of fMRI, PET and anatomical MR data, both in healthy and pathologically altered brains.     

Sensitivity of human auditory evoked potentials to the harmonicity of complex tones: evidence for dissociated cortical processes of spectral and periodicity analysis

A strong subjective tendency exists for simultaneous sound frequencies forming an harmonic series (integer multiples of the fundamental) to "group" together into a unified auditory percept whose pitch is similar to that of the fundamental. The aim of the study was to determine whether cortical auditory evoked potentials (AEPs) to complex tones differ according to whether the component frequencies of the stimuli are harmonically related or not. AEPs were recorded to continuous complex tones comprising four or more sinusoids. The vertex-maximal "change-potentials" (CP1, CN1, CP2), recorded to a stimulus cycle comprising one harmonic and five inharmonic complexes changing every second, showed no sensitivity to harmonicity, although an additional mismatch negativity was possibly present to the harmonic complex. In a second study the CP2 was significantly attenuated when an harmonic complex changed to a new one in the presence of an unchanging sinusoidal background tone, harmonically related to the first complex but not to the second, and thus becoming perceptually distinct. This, however, might be caused by lateral inhibitory effects not related to harmonicity. In a third experiment, when four concurrent sinusoidal tones came to rest on steady frequencies after a 5-s period of 16/s pseudo-random frequency changes, fronto-centrally maximal "mismatch-potentials" (MN1, MP2), were recorded. Both the MN1 and the MP2 were significantly shorter in latency when the steady frequencies formed an harmonic complex. Since the harmonic complex had a short overall periodicity, equal to that of the fundamental, while that of the inharmonic complex was much longer, the effect might be explained if the latencies of the mismatch-potential are related to periodicity. The perceptual grouping of harmonically related frequencies appears not to be a function of spectral domain analysis, reflected in the change-potentials, but of periodicity analysis, reflected in the mismatch-potentials Electronic Publication     

Acetylcholine innervation of sensory and motor neocortical areas in adult cat: a choline acetyltransferase immunohistochemical study

Light microscopic choline acetyltransferase (ChAT) immunocytochemistry was used to examine the distribution of the acetylcholine innervation in primary motor (4γ) and sensory (3a, 3b, 41 and 17) cortical areas of adult cat. In every area, scattered immunoreactive cell bodies were present and a relatively dense meshwork of ChAT immunoreactive axons pervaded the whole cortical thickness. These axons were generally thin and bore innumerable varicosities of different sizes. A few thicker and smoother fibers and occasional clusters of unusually large varicosities were also visible. Overall, area 17 was less densely innervated than the other areas. In each area, layer I showed the densest innervation. Innervation of underlying layers was rather uniform in area 17, but patterned in other areas. In areas 4γ and 3a, layers II, upper III and V showed preferential innervation. Innervation of layer IV was the strongest in areas 3b and 41. Area 3a was transitional between 4γ and 3b. Except in area 17, the laminar pattern of acetylcholinesterase staining was consistent with that of ChAT. In the light of current data on the distribution of this cortical innervation in different species, and of its presumed ultrastructural features, it appears likely that such regional and laminar features subtend widespread, modulatory roles of ACh.     

Automatic cortical responses to sound movement: a magnetoencephalography study

The aim of the present study was to clarify what change detection process leads to the elicitation of the auditory change-sensitive N1ms using magnetoencephalography (MEG). We brought our attention to whether these N1ms would be elicited if physical changes to the stimulus are eliminated. For this purpose, sound movement (SM), which entails a very subtle change only to the manner of stimuli presentation, was used in the present study. SM presentation was achieved by inserting an interaural time difference to one ear. The results indicate that both SM and the onset of the control stimulus (ON) elicited MEG responses at the superior temporal gyrus (STG) of both hemispheres. ON-N1m peak latencies were significantly shorter than those of SM-N1m as well. Interestingly, the pre-event (ON or SM) length (PreEL) was a significant factor determining the amplitude of the STG activity. Due to these findings, we hypothesize that both ON and SM activate similar groups of neurons or even an identical group of neurons. In addition, since correlations between PreEL and ON/SM-N1m amplitude exist, it is suggestible that N1m is not merely a nonspecific automatic response to physical change, but rather a much more sophisticated change-sensitive response employing a memory mechanism.     

Ultrastructural features of acute monoblastic leukaemia cells: A multivariate morphometric analysis

Summary Morphometric studies were carried out on five ultrastructural measures of size or quantity of some of the intracellular organelles in monoblasts obtained from six patients diagnosed as having acute monoblastic leukaemia and also on monocytes from six normal controls. The morphometric measures were analysed using a one way multivariate analysis of variance (MANOVA) to see whether acute monoblastic leukaemic cells differed from those of normals. It was found that there was a highly significant decrease both in the surface to volume ratio of mitochondria and also in the surface to volume ratio of the nucleus. The possible physiological significance of these structural changes is stressed.     

脑皮质发育不良性难治性癫痫57例临床病理分析

目的探讨难治性癫痫病灶手术切除患者,经病理诊断为脑皮质发育不良病例的临床病理特点。方法对57例手术切除脑癫痫病灶新鲜标本先进行测量,后切开用10％中性缓冲福尔马林溶液固定,石蜡切片,常规染色、特染及免疫组化染色,详细形态学观察。按脑皮质发育不良的病理诊断标准进行分类,探讨各种类型临床病理学特点。结果在57例中,皮质轻度发育不良（mildMCD）9例;局灶性皮层发育不良（FCD）33例（ⅠA14例,ⅠB14例,ⅡA8例,ⅡB7例）;皮层瘢痕性小脑回畸形5例。应用免疫组化和特染指标协助诊断。结论本组脑皮质发育不良以FCDⅠA和ⅠB型为常见类型;类型与手术疗效有关。一些免疫组化和特染指标有助于诊断与分型。     

Responses of single neurones in cat auditory cortex to time-varying stimuli: frequency-modulated tones of narrow excursion

Summary In the primary auditory cortex of cats anaesthetized with nitrous oxide, single neurones were examined with respect to their responses to tone bursts and linear modulations of the frequency of an on-going continuous tone. Using FM ramps of 2.0 kHz excursion and varying centre frequency, each of 39 neurones was examined for its preference for the direction of frequency change of a ramp whose centre frequency was varied in and around the neurone's response area. Direction preference was strictly associated with the slopes of the cell's spike count-versus-frequency function over the frequency range covered by the ramp. Preferences for upward- and downward-directed ramps were associated with the low- and high-frequency slopes of the spike count function, respectively. The strength of the cell's direction preference was associated with the relative steepness of the spike count function over the frequency range covered by the ramp. The timing of discharges elicited by the frequency modulations was found to be the sum of the cell's latent period for tone bursts plus the time after ramp onset that the stimulus frequency fell within the neurone's response area. The implications of these data for the processing of narrow and broad frequency-modulated ramps are discussed.     

Auditory Detection of Motion Velocity in Humans: a Magnetoencephalographic Study

No HeadingSummary: To investigate the cerebral mechanisms of auditory detection of motion velocity in the human brain, neuromagnetic fields elicited by six moving sounds and one stationary sound were investigated with a whole-cortex magnetoencephalography (MEG) system. The stationary sound evoked only one clear response at a latency of 109±6 ms (first response, or M100), but the six moving sounds evoked two clear responses: an earlier response at a latency of 116±7 ms (M100) and a later response at a latency ranging from 180 to 760 ms (magnetic motion response, or MM). The latency and amplitude of the MM were inversely related to the velocity of the moving sounds (p<0.02). The magnetic source of MM was related to the velocity of the moving sounds (p<0.05). A dynamic neuromagnetic response, MM, was elicited by the moving sounds, which likely encoded the neural processing of auditory detection of motion velocity. A specific neural network that processes the motion velocity in the human brain probably includes the bilateral superior temporal cortices and the brainstem. The left posterior and lateral part of the auditory cortex may play a pivotal role in the auditory detection of motion velocity.We thank Dr. Paul Babyn for his help and suggestions in these experiments. This paper was prepared with the assistance of Prof. Sharon Nancekivell, medical editor, Guelph, Ontario, Canada. This study was partially supported by the Savoy Foundation (Research Grant 77227).     

Auditory corticocortical interconnections in the cat: evidence for parallel and hierarchical arrangement of the auditory cortical areas

Summary The origin and laminar arrangement of the homolateral and callosal projections to the anterior (AAF), primary (AI), posterior (PAF) and secondary (AII) auditory cortical areas were studied in the cat by means of electrophysiological recording and WGA-HRP tracing techniques. The transcallosal projections to AAF, AI, PAF and AII were principally homotypic since the major source of input was their corresponding area in the contralateral cortex. Heterotypic transcallosal projections to AAF and AI were seen, originating from the contralateral AI and AAF, respectively. PAF received heterotypic commissural projections from the opposite ventroposterior auditory cortical field (VPAF). Heterotypic callosal inputs to AII were rare, originating from AAF and AI. The neurons of origin of the transcallosal connections were located mainly in layers II and III (70–92%), and less frequently in deep layers (V and VI, 8–30%). Single unit recordings provided evidence that both homotypic and heterotypic transcallosal projections connect corresponding frequency regions of the two hemispheres. The regional distribution of the anterogradely labeled terminals indicated that the homotypic and heterotypic auditory transcallosal projections are reciprocal. The present data suggest that the transcallosal auditory interconnections are segregated in 3 major parallel components (AAF-AI, PAF-VPAF and AII), maintaining a segregation between parallel functional channels already established for the thalamocortical auditory interconnections. For the intrahemispheric connections, the analysis of the retrograde tracing data revealed that AAF and AI receive projections from the homolateral cortical areas PAF, VPAF and AII, whose neurons of origin were located mainly in their deep (V and VI) cortical layers. The reciprocal interconnections between the homolateral AAF and AI did not show a preferential laminar arrangement since the neurons of origin were distributed almost evenly in both superficial (II and III) and deep (V and VI) cortical layers. On the contrary, PAF received inputs from the homolateral cortical fields AAF, AI, AII and VPAF, originating predominantly from their superficial (II and III) layers. The homolateral projections reaching AII originated mainly from the superficial layers of AAF and AI, but from the deep layers of VPAF and PAF. The laminar distribution of anterogradely labeled terminal fields, when they were dense enough for a confident identification, was systematically related to the laminar arrangement of neurons of origin of the reciprocal projection: a projection originating from deep layers was associated with a reciprocal projection terminating mainly in layer IV, whereas a projection originating from superficial layers was associated with a reciprocal projection terminating predominantly outside layer IV. This laminar distribution indicates that the homolateral auditory cortical interconnections have a feed-forward/feed-back organization, corresponding to a hierarchical arrangement of the auditory cortical areas, according to criteria previously established in the visual system of primates. The principal auditory cortical areas could be ranked into 4 distinct hierarchical levels. The tonotopically organized areas AAF and AI represent the lowest level. The second level corresponds to the non-tonotopically organized area AII. Higher, the tonotopically organized areas VPAF and PAF occupy the third and fourth hierarchical levels, respectively.Abbreviations AAF anterior auditory cortical area - AI primary auditory cortical area - AII secondary auditory cortical area - BF best frequency - C cerebral cortex - CA caudate nucleus - CL claustrum - D dorsal nucleus of the dorsal division of the MGB - ea anterior ectosylvian sulcus - ep posterior ectosylviansulcus - IC internal capsule - LGN lateral geniculate nucleus - LV pars lateralis of the ventral division of the MGB - LVe lateral ventricule - M pars magnocellularis of the medial division of the MGB - MGB medial geniculate body - MGBv ventral division of the MGB - OT optic tract - OV pars ovoidea of the ventral division of the MGB - PAF posterior auditory cortical area - PH parahippocampal cortex - PO lateral part of the posterior group of thalamic nuclei - PU putamen - RE reticular complex of thalamus - rs rhinal sulcus - SG suprageniculate nucleus of the dorsal division of the MGB - ss suprasylvian sulcus - TMB tetrametylbenzidine - VBX ventrobasal complex - VLa ventrolateral complex - VL ventro-lateral nucleus of the ventral division of the MGB - WGA-HRP wheat germ agglutinin conjugated to horse-radish peroxidase - WM white matter - VPAF ventro-posterior auditory cortical area     

Cerebral cortical mechanisms of copying geometrical shapes: a multidimensional scaling analysis of fMRI patterns of activation

We used multidimensional scaling (MDS) to characterize the integrative neural mechanisms during viewing and subsequently copying nine geometrical shapes. Human subjects initially looked at a central fixation point (“rest” period), then looked at a geometrical shape (“visual” period) which they copied without visual feedback (“copying” period). BOLD signal was recorded from voxels in 28 cortical areas (14 from each hemisphere) using a 4 Tesla magnet. For each voxel, signal ratios of “Visual versus Rest” (VR), and “Copy versus Visual” (CV) were calculated and used to construct two sets of Euclidean distance dissimilarity matrices for the nine shapes, with separate matrices defined for each region of interest (ROI) across subjects. The relations of perceptual and motor aspects of the shapes to MDS dimensions and specific ROIs were assessed using stepwise multiple regressions. The optimal individually scaled (INDSCAL) solutions were 2-dimensional. For the VR condition, MDS dimensions were significantly associated with the presence of crossing in a shape (Dimension 1), and with perimeter, height, cycles, peak segment speed, and horizontal symmetry (Dimension 2). ROIs most prominently associated with these dimensions essentially comprised the medial frontal lobe bilaterally, the inferior frontal gyrus bilaterally, and the left intraparietal sulcus (Dimension 1), and visual areas, including the calcarine sulcus and cuneus bilaterally (Dimension 2). These results document the expected involvement of visual areas and support the hypothesis advanced on the basis of previous findings (Lewis et al. 2003a) that a motor rehearsal of the upcoming shape copying is occurring during this visual presentation period. For the CV condition, practically one motor feature (number of segments drawn) dominated both dimensions, with a secondary engagement of horizontal symmetry in Dimension 1. The right postcentral gyrus, right intraparietal sulcus, right superior parietal lobule and right inferior parietal lobule contributed mostly to Dimension 1; the superior frontal gyrus bilaterally, right middle frontal gyrus, left postcentral gyrus, left inferior parietal lobule contributed mostly to Dimension 2; and the left superior parietal lobule and left intraparietal sulcus contributed to both dimensions approximately equally. CV BOLD activation of ROIs contributing to Dimension 1 (or to both dimensions) was significantly associated with the number of shape segments drawn. Since the direction of movement differs in successively drawn shape segments, the number of segments (minus one) equals the number of changes in the direction of movement. We conclude that this fundamental spatial motor aspect of drawing geometrical shapes is the critical variable, independent of the particular shape drawn, that dominates cortical activation during copying.