Activation of a sensorimotor pathway in response to a water temperature drop in a teleost fish.

When common carp, Cyprinus carpio L., experience a rapid temperature drop, the cerebral blood volume is strongly reduced to dampen the temperature drop in the brain. Simultaneously, the preoptic area and pituitary gland are activated to launch whole-body adaptive responses. However, the preferred reaction of fish to a temperature change is an escape reaction, which implies activation of a sensorimotor pathway. Here, we used blood oxygenation level-dependent (BOLD)- and cerebral blood volume (CBV)-weighted functional magnetic resonance imaging (fMRI) to identify a sensorimotor pathway, during a 10 degrees C temperature drop in common carp. Transient activation was observed in the region where the sensory root of the trigeminal nerve enters the brain, and in the valvula cerebelli. In both regions, metabolic activity increased (increased deoxyhemoglobin content demonstrated by a decreased BOLD signal) within 30 s after the onset of the temperature drop, peaked after 2-3 min, and then decreased, even though the temperature continued to drop for another 2 min. These brain structures appear to respond to temperature change, rather than to the absolute temperature. Thus, during a temperature drop, the sensorimotor pathway consisting of the trigeminal nerve, the primary sensory trigeminal nucleus, the valvula cerebelli and some motornuclei, is active, in line with perception of temperature change in the buccal cavity, leading to motor activity for escape. This pathway operates in parallel to an acclimation pathway, which involves the preoptic area to pituitary gland pathway.

A data post-processing protocol for dynamic MRI data to discriminate brain activity from global physiological effects.

All fMRI techniques measure stimulus induced focal metabolic and physiological changes in activated brain areas. During the entire fMRI experiment it is necessary to maintain the general physiological condition of the subject as stable as possible. This is not always an easy task. The typical block design in standard fMRI experiments minimizes most of the problems related with these general physiological changes. However in some fMRI experiments, like pharmacological MRI, the experimental setup makes the use of a blocked design impossible. Therefore signal correction algorithms have been developed to correct for these physiological signal instabilities. These algorithms often require elaborate calculation efforts and the data interpretation is often very difficult if no prior knowledge on the nature of the changes exists. In this work we present an algorithm, which has the advantage of being low in calculation effort and the resulting data after correction are easy to interpret. It makes use of a datafit between the general physiological and focal activation related signal changes to eliminate the generalized effects. This algorithm has been tested on simulated and experimentally obtained signal traces suffering both from substantial general signal changes overwhelming the smaller focal activation induced signal changes.

Comparing BOLD fMRI signal changes in the awake and anesthetized rat during electrical forepaw stimulation.

The difference between awake curarized and alpha-chloralose anesthetized animals was studied with respect to the BOLD signal response in an fMRI experiment. By studying the activation of the cortex upon electrical forepaw stimulation in the same rat, but following consecutively applied curarization and alpha-chloralose anesthesia protocols, it was possible to compare quantitatively the effect of both immobilization protocols on the fMRI data. The largest BOLD signal change as a result of forepaw stimulation was found in the awake condition, however the activated areas are less specific than those in the anesthetized state leaving it more difficult to interpret.

A patchy horizontal organization of the somatosensory activation of the rat cerebellum demonstrated by functional MRI.

Blood oxygenation level dependent contrast (BOLD) functional MRI (fMRI) responses, in a 7-T magnet, were observed in the cerebellum of alpha-chloralose anaesthetized rats in response to innocuous electrical stimulation of a forepaw or hindpaw. The responses were imaged in both coronal and sagittal slices which allowed for a clear delineation and localization of the observed activations. We demonstrate the validity of our fMRI protocol by imaging the responses in somatosensory cortex to the same stimuli and by showing reproducibility of the cerebellar responses. Widespread bilateral activations were found with mainly a patchy and mediolateral band organization, more pronounced ipsilaterally. Possible parasagittal bands were observed only in contralateral lobule VI. There was no overlap between the cerebellar activations caused by forepaw and hindpaw stimuli. The overall horizontal organization of these responses was quite remarkable. For both stimulation paradigms most of the activation patches were positioned in either a rostral or caudal broad plane running anteroposteriorly through both anterior and posterior cerebellum. The rostral planes were completely separated, with the forepaw activation closer to the surface, while the caudal plane was common to both stimulation protocols. We relate our findings to the known projection patterns of spinocerebellar and cuneocerebellar mossy fibres, and to human fMRI studies.