Humans can acquire appropriate behaviors that maximize rewards on a trial-and-error basis. Recent electrophysiological and imaging studies have demonstrated that neural activity in the midbrain and ventral striatum encodes the error of reward prediction. However, it is yet to be examined whether the striatum is the main locus of reward-based behavioral learning. To address this, we conducted functional magnetic resonance imaging (fMRI) of a stochastic decision task involving monetary rewards, in which subjects had to learn behaviors involving different task difficulties that were controlled by probability. We performed a correlation analysis of fMRI data by using the explanatory variables derived from subject behaviors. We found that activity in the caudate nucleus was correlated with short-term reward and, furthermore, paralleled the magnitude of a subject's behavioral change during learning. In addition, we confirmed that this parallelism between learning and activity in the caudate nucleus is robustly m...

The pattern and role of brain plasticity in stroke recovery has been incompletely characterized. Both ipsilesional and contralesional changes have been described, but it remains unclear how these relate to functional recovery. Our goal was to correlate brain activation patterns with tissue damage, hemodynamics, and neurologic status after temporary stroke, using functional magnetic resonance imaging (fMRI). Transverse relaxation time (T2)-weighted, diffusion-weighted, and perfusion MRI were performed at days 1 ( n = 7), 3 ( n = 7), and 14 ( n = 7) after 2 hr unilateral middle cerebral artery occlusion in rats. Functional activation and cerebrovascular reactivity maps were generated from contrast-enhanced fMRI during forelimb stimulation and hypercapnia, respectively. Before MRI, rats were examined neurologically. We detected loss of activation responses in the ipsilesional sensorimotor cortex, which was related to T2 lesion size ( r = −0.858 on day 3, r = −0.979 on day 14; p < 0.05). Significant activation...

The Wisconsin Card Sorting Task (WCST) has been used to assess dysfunction of the prefrontal cortex and basal ganglia. Previous brain imaging studies have focused on identifying activity related to the set-shifting requirement of the WCST. The present study used event-related functional magnetic resonance imaging (fMRI) to study the pattern of activation during four distinct stages in the performance of this task. Eleven subjects were scanned while performing the WCST and a control task involving matching two identical cards. The results demonstrated specific involvement of different prefrontal areas during different stages of task performance. The mid-dorsolateral prefrontal cortex (area 9/46) increased activity while subjects received either positive or negative feedback, that is at the point when the current information must be related to earlier events stored in working memory. This is consistent with the proposed role of the mid-dorsolateral prefrontal cortex in the monitoring of events in working mem...

The spatial organization of the brain's object and face representations in the temporal lobe is critical for understanding high-level vision and cognition but is poorly understood. Recently, exciting progress has been made using advanced imaging and physiology methods in humans and nonhuman primates, and the combination of such methods may be particularly powerful. Studies applying these methods help us to understand how neuronal activity, optical imaging, and functional magnetic resonance imaging signals are related within the temporal lobe, and to uncover the fine-grained and large-scale spatial organization of object and face representations in the primate brain.

Three macaque monkeys and 13 healthy human volunteers underwent diffusion tensor MRI with a 3 Tesla scanner for diffusion tract tracing (DTT) reconstruction of callosal bundles from different areas. In six macaque monkeys and three human subjects, the length of fiber tracts was obtained from histological data and combined with information on the distribution of axon diameter, so as to estimate callosal conduction delays from different areas. The results showed that in monkeys, the spectrum of tract lengths obtained with DTT closely matches that estimated from histological reconstruction of axons labeled with an anterogradely transported tracer. For each sector of the callosum, we obtained very similar conduction delays regardless of whether conduction distance was obtained from tractography or from histological analysis of labeled axons. This direct validation of DTT measurements by histological methods in monkeys was a prerequisite for the computation of the callosal conduction distances and delays in hum...

The present study aims to verify and validate fMRI as a new in-vivo tool for neuro-cognitive research on songbirds. Specialized brain structures allow songbirds to recognize acoustic signals, and allow them to communicate in spite of their natural noisy environment. One of these brain areas, the caudomedial nidopallium (NCM), shows a significant immediate-early-gene ZENK response when a bird hears a species-specific song. NCM is thought to extract biologically relevant information in the acoustic signal, for instance the species-specific identity, and to transmit this information to other brain structures. Background noise can be an obstacle to the successful perception of significant information in acoustic signals. Vignal et al. (Behav Brain Res, 153, 241-48) demonstrated that the song-induced genic activation in the NCM remains stable against very high levels of a broadband masking noise, as far as the stimuli elicited a behavioral response (i.e. signal recognition remains possible for the bird). A prev...

Functional MRI is a non-invasive technique that indirectly detects areas of neuronal activity by observing local changes in blood oxygen. Until recently fMRI has been used only for brain imaging, however, it has since been applied to the spinal cord (spinal fMRI). The relationship between areas of fMRI activity and areas of neuronal activity must be verified by comparison with gold standards in order for spinal fMRI to become more widely accepted. In the present study we compare areas of fMRI activity with areas of extracellular field potentials during noxious electrical stimulation of the hind paw in rats. Halothane-anesthetized rats were placed supine on a quadrature surface coil tuned and matched to 300 MHz. Six, 2 mm thick slices were centred on the vertebra and intervertebral discs between T12 and L1. Three functional imaging experiments on each animal were performed using electrical stimulation (~ 7 mA) delivered by two silver needle electrodes inserted subcutaneously in the dorsal surface of the rig...

The injection of kainic acid (KA) into rat elicits brain damages, including hippocampus, which mimic human temporal lobe epilepsy. Electrophysiological studies evidenced that KA induces epileptiform seizures first in hippocampal CA3 within 1 hr and then propagates to CA1 and other limbic structures. To gain further understanding of the hippocampal activation underlying KA-induced seizures, the aims of the present study are (1) to employ high resolution diffusion-weighted imaging (DWI) and T2-weighted imaging (T2WI) at high magnetic field (7 Tesla) to investigate the temporal evolution of hippocampal abnormalities induced by KA and (2) to investigate whether KA-induced CA3 neuronal activity can be detected using manganese (Mn2+)-enhanced MRI. DWI, T2WI and T1-weighted imaging (T1WI) were acquired before and 2 hr, 1 day¡V7 days after KA intravenous injection. The results showed that, in the dendrites of CA3 pyramidal cells, the hyperintensities of DWI and T2WI were both observed within 2 hr, indicating the f...

Brain [Na+] has been proposed to assess insult duration in evolving stroke (Wang et al, 2000 Stroke 31,1386). Stroke localization and the type of local blood supply may modify this relation. We hypothesized that the time course of [Na+] in cortical stroke (COR) where collateral circulation is present is different than in caudoputamen stroke (CP) where collateral circulation is absent. In Sprague-Dawley rats (~340 g) under isoflurane anesthesia focal ischemia was induced either by occlusion of the distal middle cerebral artery and both common carotid arteries or by insertion of an intraluminal suture through the internal carotid artery. 3D [Na+] data were obtained on a 3 T whole body scanner (GE MS) using a dual-tuned (23Na/1H), dual-quadrature birdcage RF coil. The infarct was located using ADC 1H images. [Na+] maps (twisted projection) were acquired every 5.3 min from which the [Na+] in % change from the average in normal cortex was measured vs. time after occlusion, Ta, in hours. The rate of [Na+] increa...

An event-related functional magnetic resonance imaging study of prefrontal cortex was conducted during which subjects performed a visual “oddball” target detection task. Exemplars of three stimulus categories were presented at a rate of one per 1.5 sec for 10 runs, each consisting of 132 trials. Standards were color squares of varying sizes that were presented on ∼92% of trials. Targets were color circles of varying sizes presented irregularly on ∼4% of trials. Novels were pictures of everyday objects that were also presented irregularly on ∼4% of trials. Ten subjects participated in two separate sessions in which they were required to count mentally or to push a button whenever a target appeared. Targets evoked activation within prefrontal cortex, primarily within the middle frontal gyri (MFG). This MFG activation did not differ as a function of the required response. Novels did not evoke significant activity within this region despite evidence from a separate behavioral and event-related potential study ...