The Journal of neuroscience : the official journal of the Society for Neuroscience
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Comparative Study
Occipital transcranial magnetic stimulation has opposing effects on visual and auditory stimulus detection: implications for multisensory interactions.
Multisensory interactions occur early in time and in low-level cortical areas, including primary cortices. To test current models of early auditory-visual (AV) convergence in unisensory visual brain areas, we studied the effect of transcranial magnetic stimulation (TMS) of visual cortex on behavioral responses to unisensory (auditory or visual) or multisensory (simultaneous auditory-visual) stimulus presentation. Single-pulse TMS was applied over the occipital pole at short delays (30-150 ms) after external stimulus onset. ⋯ The beneficial interaction effect of combined unisensory auditory and TMS-induced visual cortex stimulation matched and was correlated with the RT-facilitation after external multisensory AV stimulation without TMS, suggestive of multisensory interactions between the stimulus-evoked auditory and TMS-induced visual cortex activities. A follow-up experiment showed that auditory input enhances excitability within visual cortex itself (using phosphene-induction via TMS as a measure) over a similarly early time-window (75-120 ms). The collective data support a mechanism of early auditory-visual interactions that is mediated by auditory-driven sensitivity changes in visual neurons that coincide in time with the initial volleys of visual input.
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Comparative Study
Synaptic connections between layer 5B pyramidal neurons in mouse somatosensory cortex are independent of apical dendrite bundling.
Rodent somatosensory barrel cortex is organized both physiologically and anatomically in columns with a cross-sectional diameter of 100-400 microm. The underlying anatomical correlate of physiologically defined, much narrower minicolumns (20-60 microm in diameter) remains unclear. The minicolumn has been proposed to be a fundamental functional unit in the cortex, and one anatomical component of a minicolumn is thought to be a cluster of pyramidal cells in layer 5B (L5B) that contribute their apical dendrite to distinct bundles. ⋯ L5B pyramids within and between clusters have similar connection probabilities and unitary EPSP amplitudes. Furthermore, intrinsically bursting and regular spiking pyramidal cells were both present within the same cluster. In conclusion, intrinsic electrical excitability and the properties of synaptic connections between this subtype of L5B pyramidal cells are independent of the cell clusters defined by bundling of their apical dendrites.
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Comparative Study
Attentional modulation of spatial integration of pain: evidence for dynamic spatial tuning.
In many sensory modalities, afferent processing is dynamically modulated by attention and this modulation produces altered sensory experiences. Attention is able to alter perceived pain, but the mechanisms involved in this modulation have not been elucidated. To determine whether attention alters spatial integration of nociceptive information, subjects were recruited to evaluate pain from pairs of noxious/innocuous thermal stimuli during different spatial attentional tasks. ⋯ In contrast, directed attention enhanced pain intensity by partially integrating both stimuli. This dynamic modulation of spatial integration indicates that attention alters spatial dimensions of afferent nociceptive processing to optimize the perceptual response to input from a particular body region or stimulus feature. This dynamic spatial tuning of nociceptive processing provides a new conceptual insight into the functional significance of endogenous pain inhibitory and facilitatory mechanisms.
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Action selection requires choosing one of all the possible conflicting action plans that are available. There is currently a debate as to whether the dorsal medial frontal cortex (dMFC) merely detects or actively resolves response conflict. We used combined on-line transcranial magnetic stimulation and electroencephalographic recording (TMS-EEG) to test whether human dMFC plays a critical causal role in conflict resolution, and whether the mechanism for such a function is via interactions with primary motor cortex. ⋯ TMS disrupted performance by selectively increasing error rates on contralateral (right hand) incongruent trials. TMS also only modulated the LRP on incongruent trials, causing an increased positive deflection (associated with preparation of the incorrect response) starting 180 ms after visual stimulus onset. TMS of a control site did not interfere with behavior or motor cortical activity. dMFC has a direct causal role in resolving conflict during action selection, and the mechanism involves the top-down modulation of primary motor cortical activity.
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Comparative Study
Cyclooxygenase-1-derived prostaglandins in the periaqueductal gray differentially control C- versus A-fiber-evoked spinal nociception.
Nonsteroidal anti-inflammatory drugs (NSAIDs) exert analgesic effects by inhibiting peripheral cyclooxygenases (COXs). It is now clear that these drugs also have central actions that include the modulation of descending control of spinal nociception from the midbrain periaqueductal gray (PAG). Descending control is a powerful determinant of the pain experience and is thus a potential target for analgesic drugs, including COX inhibitors. ⋯ The results significantly advance our understanding of the central mechanisms underlying the actions of NSAIDs and prostaglandins by demonstrating that (1) in the PAG, it is COX-1 and not COX-2 that is responsible for acute antinociceptive effects of NSAIDs in vivo; (2) these effects are only evoked from the opioid-sensitive ventrolateral PAG; and (3) prostaglandins in the PAG exert tonic facilitatory control that targets C- rather than A-fiber-mediated spinal nociception. This selectivity of control is of particular significance given the distinct roles of A- and C-nociceptors in acute and chronic pain. Thus, effects of centrally acting prostaglandins are pivotal, we suggest, to both the understanding of nociceptive processing and the development of new analgesic drugs.