Biomedical subjects

Jorge Mariño

Publications and source records attributed to Jorge Mariño.

8 recordsLinked to original sources

PubMed2006

Changes in visual responses in the feline dLGN: selective thalamic suppression induced by transcranial magnetic stimulation of V1.

Transcranial magnetic stimulation (TMS) of the cortex can modify activity noninvasively and produce either excitatory or inhibitory effects, depending on stimulus parameters. Here we demonstrate controlled inhibitory effects on the large corticogeniculate feedback pathway from primary visual cortex to cells of the dorsal lateral geniculate nucleus (dLGN) that are focal and reversible-induced by either single pulses or trains of pulses of TMS. These effects selectively suppress the sustained component of responses to flashed spots or moving grating stimuli and are the result of loss of spikes fired in tonic mode, whereas the number of spikes fired in bursts remain the same. We conclude that acute inactivation of the corticogeniculate downflow selectively affects the tonic mode. We found no evidence to suggest that cortical inactivation increased burst frequency.

Action Potentials↗

PubMed2006

Cortical modulation of dorsal column nuclei: a computational study.

We present a computational study aimed at exploring the sensorimotor cortex modulation of the behaviour of dorsal column nuclei, specifically the impact of synaptic parameters, during both sleep and waking conditions. On the basis of the circuit proposed by Canedo et al. (2000), we have developed realistic computational models that have been tested with simultaneous electrocorticographic as well as intracellular cuneate recordings performed in anaesthetized cats. The results show that, (1) under sleep conditions, the model can block the transmission of afferent sensory information and, (2) operations expected during wakefulness, such as filtering and facilitation, can be performed if synaptic parameters are appropriately tuned.

Animals↗

PubMed2005

Local networks in visual cortex and their influence on neuronal responses and dynamics.

Networks of neurons in the cerebral cortex generate complex outputs that are not simply predicted by their inputs. These emergent responses underlie the function of the cortex. Understanding how cortical networks carry out such transformations requires a description of the responses of individual neurons and of their networks at multiple levels of analysis. We focus on orientation selectivity in primary visual cortex as a model system to understand cortical network computations. Recent experiments in our laboratory and others provide significant insight into how cortical networks generate and maintain orientation selectivity. We first review evidence for the diversity of orientation tuning characteristics in visual cortex. We then describe experiments that combine optical imaging of orientation maps with intracellular and extracellular recordings from individual neurons at known locations in the orientation map. The data indicate that excitatory and inhibitory synaptic inputs are summed across the cortex in a manner that is consistent with simple rules of integration of local inputs. These rules arise from known anatomical projection patterns in visual cortex. We propose that the generation and plasticity of orientation tuning is strongly influenced by local cortical networks-the diversity of these properties arises in part from the diversity of neighbourhood features that derive from the orientation map.

Animals↗

PubMed2005

Invariant computations in local cortical networks with balanced excitation and inhibition.

Cortical computations critically involve local neuronal circuits. The computations are often invariant across a cortical area yet are carried out by networks that can vary widely within an area according to its functional architecture. Here we demonstrate a mechanism by which orientation selectivity is computed invariantly in cat primary visual cortex across an orientation preference map that provides a wide diversity of local circuits. Visually evoked excitatory and inhibitory synaptic conductances are balanced exquisitely in cortical neurons and thus keep the spike response sharply tuned at all map locations. This functional balance derives from spatially isotropic local connectivity of both excitatory and inhibitory cells. Modeling results demonstrate that such covariation is a signature of recurrent rather than purely feed-forward processing and that the observed isotropic local circuit is sufficient to generate invariant spike tuning.

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PubMed2003

Nitric oxide-mediated cortical activation: a diffuse wake-up system.

Nitric oxide (NO) has been implicated in some of the central pathways engaged in the regulation of the sleep-wake cycle. The existence of nitric oxide synthase (NOS) in the cholinergic basal forebrain (BF) cells projecting to the cortex suggests a role for NO in the activation induced by the BF during arousal. We tested, in the anesthetized cat, the hypothesis that inhibition of NOS would decrease the ability of BF cholinergic fibers to induce cortical activation. In control conditions, BF stimulation evoked an awake-like EEG pattern (i.e., a decrease in the low-frequency-high-amplitude oscillatory activity and an increase in the high-frequency-low-amplitude activity). After blocking NOS activity, the capacity of BF stimulation to induce cortical activation was strongly impaired. Furthermore, voltammetric measurements of NO levels revealed an increase in cortical NO after BF stimulation, also blocked by systemic NOS inhibition. These results indicate that the blockade of NOS activity significantly reduces the ability of BF stimulation to induce changes in the EEG pattern and suggest a role for NO in the BF-cholinergic system implicated in arousal mechanisms.

Animals↗

PubMed2003

A computational model of cuneothalamic projection neurons.

The dorsal column nuclei, cuneatus and gracilis, play a fundamental role in the processing and integration of somesthetic ascending information. Intracellular and patch-clamp recordings obtained in cat in vivo have shown that cuneothalamic projection neurons present two modes of activity: oscillatory and tonic (Canedo et al 1998 Neuroscience 84 603-17). The former is the basis of generating, in sleep and anaesthetized states, slow, delta and spindle rhythms under the control of the cerebral cortex (Mariño et al 2000 Neuroscience 95 657-73). The latter is needed, during wakefulness, to process somesthetic information in real time. To study this behaviour we have developed the first realistic computational model of the cuneothalamic projection neurons. The modelling was guided by experimental recordings, which suggest the existence of hyperpolarization-activated inward currents, transient low- and high-threshold calcium currents, and calcium-activated potassium currents. The neuronal responses were simulated during (1) sleep, (2) transition from sleep to wakefulness and (3) wakefulness under both excitatory and inhibitory synaptic input. In wakefulness the model predicts a set of synaptically driven firing modes that could be associated with information processing strategies in the middle cuneate nucleus.

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PubMed2002

Synaptic integration by V1 neurons depends on location within the orientation map.

Neurons in the primary visual cortex (V1) are organized into an orientation map consisting of orientation domains arranged radially around "pinwheel centers" at which the representations of all orientations converge. We have combined optical imaging of intrinsic signals with intracellular recordings to estimate the subthreshold inputs and spike outputs of neurons located near pinwheel centers or in orientation domains. We find that neurons near pinwheel centers have subthreshold responses to all stimulus orientations but spike responses to only a narrow range of orientations. Across the map, the selectivity of inputs covaries with the selectivity of orientations in the local cortical network, while the selectivity of spike outputs does not. Thus, the input-output transformation performed by V1 neurons is powerfully influenced by the local structure of the orientation map.

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PubMed1999

Sensorimotor Integration at the Dorsal Column Nuclei.

Interaction among primary afferents, corticofugal fibers, and intrinsic elements allows for sensorimotor integration at the dorsal column nuclei. The interneurons permit the spatial localization, the recurrent collaterals synchronize the activity of projecting cells with overlapping receptive fields, and the corticofugal fibers induce a central zone of activity surrounded by a peripheral zone of inhibition.

Journal Article↗