Neuro-evolutionary evidence for a universal fractal primate brain shape

The primate cerebral cortex can take on a bewildering diversity of shapes and sizes within and across species, whilst maintaining archetypal qualities that make it instantly recognisable as a "brain". Here we present a new way of expressing the shape of a cortex explicitly as the hierarchical composition of structures across spatial scales. In computational simulations, as one successively removes sulci and gyri smaller than a specified scale, the cortices of 11 primate species are gradually coarse-grained into less folded brains until lyssencephaly (no folding). We show that this process, in all cases, occurs along a common scale-free morphometric trajectory overlapping with other mammalian species, indicating that these cortices are not only approximately fractal in shape, but also, strikingly, are approximations of the same archetypal fractal shape. These results imply the existence of a single universal gyrification mechanism that operates in a scale-free manner on cortical folds of all sizes, and that there are surprisingly few effective degrees of freedom through which cortical shapes can be selected for by evolution. Finally, we demonstrate that this new understanding can be of practical use: biological processes can now be interrogated in a highly scale-dependent way for increased sensitivity and precision. To our knowledge, this is the most parsimonious universal description of the brain's shape that is at the same time mechanistically insightful, practically useful, and in full agreement with empirical data across species and individuals

Own Song Selectivity in the Songbird Auditory Pathway: Suppression by Norepinephrine

Like human speech, birdsong is a learned behavior that supports species and individual recognition. Norepinephrine is a catecholamine suspected to play a role in song learning. The goal of this study was to investigate the role of norepinephrine in bird's own song selectivity, a property thought to be important for auditory feedback processes required for song learning and maintenance.Using functional magnetic resonance imaging, we show that injection of DSP-4, a specific noradrenergic toxin, unmasks own song selectivity in the dorsal part of NCM, a secondary auditory region.The level of norepinephrine throughout the telencephalon is known to be high in alert birds and low in sleeping birds. Our results suggest that norepinephrine activity can be further decreased, giving rise to a strong own song selective signal in dorsal NCM. This latent own song selective signal, which is only revealed under conditions of very low noradrenergic activity, might play a role in the auditory feedback and/or the integration of this feedback with the motor circuitry for vocal learning and maintenance

Functional MRI of Auditory Responses in the Zebra Finch Forebrain Reveals a Hierarchical Organisation Based on Signal Strength but Not Selectivity

BACKGROUND: Male songbirds learn their songs from an adult tutor when they are young. A network of brain nuclei known as the 'song system' is the likely neural substrate for sensorimotor learning and production of song, but the neural networks involved in processing the auditory feedback signals necessary for song learning and maintenance remain unknown. Determining which regions show preferential responsiveness to the bird's own song (BOS) is of great importance because neurons sensitive to self-generated vocalisations could mediate this auditory feedback process. Neurons in the song nuclei and in a secondary auditory area, the caudal medial mesopallium (CMM), show selective responses to the BOS. The aim of the present study is to investigate the emergence of BOS selectivity within the network of primary auditory sub-regions in the avian pallium. METHODS AND FINDINGS: Using blood oxygen level-dependent (BOLD) fMRI, we investigated neural responsiveness to natural and manipulated self-generated vocalisations and compared the selectivity for BOS and conspecific song in different sub-regions of the thalamo-recipient area Field L. Zebra finch males were exposed to conspecific song, BOS and to synthetic variations on BOS that differed in spectro-temporal and/or modulation phase structure. We found significant differences in the strength of BOLD responses between regions L2a, L2b and CMM, but no inter-stimuli differences within regions. In particular, we have shown that the overall signal strength to song and synthetic variations thereof was different within two sub-regions of Field L2: zone L2a was significantly more activated compared to the adjacent sub-region L2b. CONCLUSIONS: Based on our results we suggest that unlike nuclei in the song system, sub-regions in the primary auditory pallium do not show selectivity for the BOS, but appear to show different levels of activity with exposure to any sound according to their place in the auditory processing stream

An Open Resource for Non-human Primate Imaging.

Non-human primate neuroimaging is a rapidly growing area of research that promises to transform and scale translational and cross-species comparative neuroscience. Unfortunately, the technological and methodological advances of the past two decades have outpaced the accrual of data, which is particularly challenging given the relatively few centers that have the necessary facilities and capabilities. The PRIMatE Data Exchange (PRIME-DE) addresses this challenge by aggregating independently acquired non-human primate magnetic resonance imaging (MRI) datasets and openly sharing them via the International Neuroimaging Data-sharing Initiative (INDI). Here, we present the rationale, design, and procedures for the PRIME-DE consortium, as well as the initial release, consisting of 25 independent data collections aggregated across 22 sites (total = 217 non-human primates). We also outline the unique pitfalls and challenges that should be considered in the analysis of non-human primate MRI datasets, including providing automated quality assessment of the contributed datasets

Perception auditive et substitution sensorielle chez la personne voyante et non-voyante : approche neuro-éthologique

Sensory substitution refers to the use of one sensory modality to supply information normally gathered by another sense. In the case of blindness, visual information can be transmitted through the auditory or tactile channels. An auditory-for-visual substitution prosthesis has been developed in the Neural Rehabilitation Engineering Laboratory. During this PhD, we were interested in both the neural bases of auditory perception and the learning mechanisms of prosthesis use. This PhD work has shown the involvement of the occipital cortex during auditory processing in sighted subjects. It has allowed us to specify the organisation and the functionality of the occipital cortex in blind subjects. This PhD has also allowed us to define the learning mechanisms of prosthesis use. Finally, it has demonstrated the involvement of the visual areas during prosthesis use in blindfolded sighted subjects. All these results led us to suggest a general scheme of the neural mechanisms underlying the sensory substitution phenomenon. On the one hand, the visual mental imagery process seems to induce the recruitment of visual areas during the prosthesis use in sighted subjects. This process would induce a 'visual-like perception'. The contribution of mental imagery seems to increase through learning. On the other hand, auditory processing of stimuli coming from the prosthesis seems to be able to induce the recruitment of visual areas in the blindfolded sighted subjects. Both these mechanisms, mental imagery and auditory processing, may be involved in the recruitment of visual areas previously observed in blind subjects during the prosthesis use.La substitution sensorielle est une technique de réhabilitation qui vise à fournir des informations normalement transmises par une modalité sensorielle déficiente par le biais d'une autre modalité. Dans le cadre de la cécité, il s'agit de transmettre des informations visuelles via le canal auditif ou tactile. Une prothèse visuo-auditive a été développée au sein du laboratoire de Génie de la Réhabilitation Neurale. Au cours de cette thèse, nous nous sommes intéressés d'une part aux bases neurales de la perception auditive et d'autre part aux mécanismes d'apprentissage de l'utilisation de cette prothèse visuo-auditive. Cette thèse a permis de montrer chez le sujet voyant l'implication du cortex occipital dans le traitement de stimuli auditifs et de préciser l'organisation et le fonctionnement du cortex occipital chez le sujet non-voyant précoce. Elle a également permis de définir les mécanismes d'apprentissage de l'utilisation de la prothèse et a mis en évidence le recrutement des aires visuelles lors de l'utilisation de la prothèse chez le sujet voyant ayant les yeux bandés. L'ensemble de ces résultats nous a amené à proposer un schéma général des mécanismes neuraux sous-tendant le phénomène de substitution sensorielle. D'une part, un processus d'imagerie mentale visuelle semble être responsable du recrutement des aires visuelles chez le sujet voyant lors de l'utilisation de la prothèse. Ce processus d'imagerie induirait une perception « pseudo-visuelle ». L'importance de l'imagerie mentale visuelle semble augmenter au cours de l'apprentissage. D'autre part, le traitement auditif des stimuli provenant de la prothèse semble également pouvoir induire le recrutement des aires visuelles chez les sujets voyants. Ces deux mêmes mécanismes, imagerie mentale et traitement auditif, pourraient être impliqués dans le recrutement des aires visuelles précédemment observé chez le sujet non-voyant lors de l'utilisation de la prothèse.Thèse de doctorat en sciences biomédicales (neurosciences)(SBIM 3) -- UCL, 200

What neuroimaging tells us about sensory substitution.

A major question in the field of sensory substitution concerns the nature of the perception generated by sensory substitution prostheses. Is the perception determined by the nature of the substitutive modality or is it determined by the nature of the information transmitted by the device? Is it a totally new, amodal, perception? This paper reviews the recent neuroimaging studies which have investigated the neural bases of sensory substitution. The detailed analysis of available results led us to propose a general scheme of the neural mechanisms underlying sensory substitution. Two different main processes may be responsible for the visual area recruitment observed in the different studies: cross-modality and mental (visual) imagery. Based on our results analysis, we propose that cross-modality is the predominant process in early blind subjects whereas mental imagery is predominant in blindfolded sighted subjects. This model implies that, with training, sensory substitution mainly induces visual-like perception in sighted subjects and mainly auditory or tactile perception in blind subjects. This framework leads us to make some predictions that could easily be tested

Own-song recognition in the songbird auditory pathway: selectivity and lateralization.

The songbird brain is able to discriminate between the bird's own song and other conspecific songs. Determining where in the brain own- song selectivity emerges is of great importance because experience-dependent mechanisms are necessarily involved and because brain regions sensitive to self-generated vocalizations could mediate auditory feedback that is necessary for song learning and maintenance. Using functional MRI, here we show that this selectivity is present at the midbrain level. Surprisingly, the selectivity was found to be lateralized toward the right side, a finding reminiscent of the potential right lateralization of song production in zebra finches but also of own-face and own-voice recognition in human beings. These results indicate that a midbrain structure can process subtle information about the identity of a subject through experience-dependent mechanisms, challenging the classical perception of subcortical regions as primitive and nonplastic structures. They also open questions about the evolution of the cognitive skills and lateralization in vertebrates

Neural changes in the ventral and dorsal visual streams during pattern recognition learning.

The learning process related to pattern and object recognition is difficult to study because the human brain has a remarkable capacity to recognise complex visual forms from early infancy. In the present study, we investigated on-going neural changes underlying the learning process of visual pattern recognition by means of a device substituting audition for vision. Functional MRI evidenced the gradual pattern recognition-induced recruitment of the ventral visual stream, bilaterally, from learning session 1 to session 3, and a slight decrease in these activation foci from session 3 to session 4. The initial increase in activation is thought to reflect the gradually enhanced visualisation of patterns in the subjects' mind across sessions. By contrast the subsequent decrease reported at the end of the training period is interpreted as the progressive optimisation of neuronal responses elicited by the task. Our results, in accordance with previous observations, suggest that the succession of activation increase and decrease in sensori-motor areas could be a general rule in sensory and sensori-motor learning