Elenco seminari del ciclo di seminari
“NEUROMATEMATICA ”

Rodents are emerging as increasingly popular models of visual functions. Yet, evidence that rodent visual cortex is capable of advanced visual processing, such as object recognition, is limited. In my seminar, I will describe the results of a recent study in which we have investigate how neurons located along the progression of extrastriate areas that, in the rat brain, run laterally to primary visual cortex, encode object information. We found a progressive functional specialization of neural responses along these areas, with: i) a gradual increase of receptive field size and response latency; ii) a sharp reduction of the amount of low-level, energy-related visual information encoded by neuronal firing; and iii) a substantial increase in the ability of single neurons to support discrimination of visual objects under identity-preserving transformations (e.g., position and size changes). These findings strongly argue for the existence of a rat object-processing pathway, and point to the rodents as promising models to dissect the neuronal circuitry underlying transformation-tolerant recognition of visual objects.

c

Cortical functions result from the conjoint function of different, reciprocally connected areas working together as large-scale functionally specialized networks. Architectonic, connectional, and functional data have provided evidence for functionally specialized large-scale cortical networks of the macaque brain involving temporal, parietal, and frontal areas. These networks appear to play a primary role in controlling different aspects of motor and cognitive motor functions, such as hand action organization and recognition, or oculomotor behavior and gaze processing. Based on comparison of these data with data from human studies, it is possible to argue that there is clear evidence for human counterparts of these networks. These human and macaque putatively homologue networks appear to share phylogenetically older neural mechanisms, which in the evolution of the human lineage could have been exploited and differentiated resulting in the emergence of human-specific functions higher-order cognitive functions

This talk summarizes two modeling studies on the motor cortex and the cerebellum. The motor cortex is the final cortical pathway to motor circuits in the spinal cord, but its functional role has long been debated, particularly whether the motor cortex represents movement kinematics or dynamics. To resolve this issue, I modeled the visuomotor transformation using Newton-Euler equations of motion that has been used in robotics, and proposed that neural activities in the motor cortex represent vector cross products in the equations. This model explains a wide variety of the characteristics reported in the motor cortex in a unified manner. The cerebellum is hypothesized to predict a future state of the body from a current state and a corollary discharge, the computation known as an internal forward model. Although this hypothesis has been supported from a number of clinical, psychophysical and neuroimaging studies, a direct neurophysiological evidence is missing. I analyzed firing rates of mossy fibers (cerebellar inputs), Purkinje cells (outputs from cerebellar cortex), and dentate cells (cerebellar outputs) recorded from a behaving monkey. I found that the cerebellar outputs provided predictive information about future inputs to the cerebellum, providing direct neurophysiological evidence for the forward-model hypothesis of the cerebellum. [1] Tanaka, H., & Sejnowski, T. J. (2013). Computing reaching dynamics in motor cortex with Cartesian spatial coordinates. Journal of Neurophysiology, 109(4), 1182-1201. [2] Tanaka, H., & Sejnowski, T. J. (2015). Motor adaptation and generalization of reaching movements using motor primitives based on spatial coordinates. Journal of Neurophysiology, 113(4), 1217-1233. [3] Tanaka, H., Ishikawa, T., & Kakei, S. (2019). Neural Evidence of the Cerebellum as a State Predictor. The Cerebellum, 1-23.

The activity of neurons of the medial posterior parietal area V6A in macaquemonkeys ismodulated bymany aspects of reach task. In the past, research wasmostly focused on modulating the effect of single parameters upon the activity of V6A cells. Here, we used Generalized Linear Models (GLMs) to simultaneously test the contribution of several factors upon V6A cells during a fix-to-reach task. This approach resulted in the definition of a representative ‘‘functional fingerprint’’ for each neuron. We first studied how the features are distributed in the population. Our analysis highlighted the virtual absence of units strictly selective for only one factor and revealed that most cells are characterized by ‘‘mixed selectivity.’’ Then, exploiting our GLM framework, we investigated the dynamics of spatial parameters encoded within V6A. We found that the tuning is not static, but changed along the trial, indicating the sequential occurrence of visuospatial transformations helpful to guide arm movement. Indirizzo zoom https://unibo.zoom.us/j/84150284556

This is the therd seminar of a cicle devoted to learn properties of brain neural network from neurophysiological data. It will be quite technical and open to a restricted specialistic pubblic.

This is the second seminar of a cicle devoted to learn properties of brain neural network from neurophysiological data. This seminar is quite technical and open only to a restricted specialistic pubblic.