Mechanisms underlying response dynamics in barrel cortex
- Autores: Marta Diaz Quesada
- Directores de la Tesis: Miguel Maravall Rodriguez (dir. tes.)
- Lectura: En la Universidad Miguel Hernández de Elche ( España ) en 2010
- Idioma: español
- Tribunal Calificador de la Tesis: Roberto Gallego Fernández (presid.), Luis Miguel Martínez Otero (secret.), Mathew Diamond (voc.), Rasmus Petersen (voc.), Albert Compte Braquets (voc.)
- Materias:
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- Resumen
Animals live in a dynamic world and sensory inputs unfold over time. Sensory systems make use of this temporal dimension when representing stimuli, both to encode information about the stimulus and to adjust the representation to the environment, or context, within which the stimulus is received. This thesis focuses on the mechanisms underlying the dynamics of responses in the barrel cortex, the cortical region receiving tactile stimuli from a rodent's vibrissae. Specifically, we have studied mechanisms involved in the adaptation of barrel cortex neurons to stimulus statistics. Different forms of adaptation have been described in most animal species and sensory systems, suggesting that this phenomenon is an important principle of sensory function.
In vivo, barrel cortex responses adapt to changes in the statistics of complex whisker stimuli. This adaptation involves an adjustment in the input-output tuning functions of neurons, such that their gain rescales depending on the range of the current stimulus distribution. In other sensory systems this type of adaptation has been shown to depend on intrinsic properties; however, in barrel cortex, whether intrinsic mechanisms can contribute to adaptation to stimulus statistics is unknown. To examine this, we performed whole-cell patch-clamp recordings of pyramidal cells in acute slices from rats while injecting stochastic current stimuli. We induced changes in statistical context by switching across stimulus distributions. We saw that firing rate adaptation was strongly dependent on the form of the changes in stimulus distribution. In fact, in vivo-like adaptation occurred only for rectified stimuli that maintained neurons in a persistent state of net depolarization. Under these conditions, neurons rescaled the gain of their input-output functions according to the scale of the stimulus distribution, as observed in vivo. In vivo-like adaptation and gain rescaling were present in neurons of different cortical layers. This stimulus-specific adaptation was unaffected by blockade of synaptic transmission and correlated strongly with the amplitude of calcium dependent slow afterhyperpolarizations. These results suggest that widely expressed intrinsic mechanisms participate in barrel cortex adaptation but that their recruitment is highly stimulus specific.
We also studied the short-term dynamics of TC synaptic connections. The thalamic input to layer 4 neurons dominates sensory input into the cortex. To study how the magnitude of this connection is modulated in time depending on stimulus pattern, we performed whole-cell patch-clamp recordings in TC slices. We compared responses to regular stimulation with responses to irregular, naturalistic stimulation patterns derived from thalamic recordings in vivo. Consistent with previous findings, we found that regular stimulation always generated strong short-term synaptic depression. However, naturalistic stimulation evoked more complex responses, consisting of a mixture of depression and facilitation. Short-term plasticity was diverse across different neurons. The different types of response could be found at both room temperature and physiological temperature as well as at different calcium concentrations, suggesting that they were caused by true diversity in the mechanisms underlying short-term synaptic dynamics. These results suggest a previously unsuspected diversity in the selectivity of TC responses to different temporal types of stimulation.
