Per Roland Group – University of Copenhagen

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Brain Research > Research > Per Roland Group

Research

Movie: The ΔV(t) (statistically significant p <0.01 after Bonferroni correction) in response to a bar moving downwards starting in the peripheral field of view. The retina is stationary. Note that the bar then is mapped as moving excitation over the cortex. However, at 104 ms the neurons in area s 19/21 compute an excitation far ahead of the bar mapping. After feedback to areas 17/18 this repeats here. The black holes show the electrode penetration sites along the border between areas 17 and 18 corresponding to the vertical meridian. When the spiking at any layer of the cortex becomes statistically significant (p < 0.01) the hole turns white. Note the mapping of the future bar trajectory when the bar representation on the cortex has reached the left white arrow (155 ms). Note also how the object mapping, defined by the hot spot in area 17/18 actually follows the cortical route predicted already at 160 ms. Animal 410. (From Harvey et al. 2009).

Neurodynamics

Mammalian brains have up to 3 x 1010 of neurons connected by 1015 synapses. Short axons connect neurons within cortical areas and long axons connect neurons located in different cortical areas. As long as the mammal is alive the neurons emit action potentials during deep sleep, dream sleep, and when the brain receives action potentials from the senses, when it thinks, plan and execute behavior. Ultimately, the total register of what brains can do depends on how may diverse ways action potentials can propagate though this immense network to produce equally many ways of evolving action potential and membrane dynamics. Our scientific problem is to understand how the dynamics of the communications by spiking and resulting membrane conductances drives the populations of neurons in the visual areas to reconstruct the visual scene or interpret sounds and sound sequences. In other words, we want to reveal the mechanisms of initial vision and audition - even under conditions when the reconstruction and interpretations fail. We found that the cortical neurons at the mesoscopic scale behave surprisingly well, revealing how fundamental physiological variables such as instantaneous firing rate, net-excitation and net-inhibition evolve to produce the brain’s interpretation of the physical surround in some 110-150 ms. From the observed dynamics we aim to derive principles of intra-area and inter-area dynamics. Given these principles we collaborate with computational neuroscientists and mathematicians to build models reproducing these observed dynamics in a smaller or larger scale. As some of the principles might be general, we collaborate with the other groups in the Neuronal Signaling Laboratory to test that in spinal and cerebellar networks. We also collaborate with the Brain Laboratory scientists in examining visual illusions in humans. In practice we use laminar recordings with multi-electrodes in cortical areas combined with voltage sensitive dye recordings in animal experiments.