High resolution functional MRI (fMRI) experiments were performed in human visual cortex at 0.5, 1.5, and 4 T to determine the blood oxygenation level dependent (BOLD) field strength response within regions of obvious venous vessels and cortical gray matter ("tissue"). T2*-weighted FLASH images were collected in single- and multi-echo mode and used to determine the intrinsic BOLD parameters, namely, signal-to-noise ratio (psi), the apparent transverse relaxation rate (R2*) and the change in R2* (deltaR2*) between the activated and baseline states. The authors find the average percentage signal change (deltaS/S, measured at TE = T2*) to be large in vessels (13.3 +/- 2.3%, 18.4 +/- 4.0%, and 15.1 +/- 1.2%) compared with that in tissue (1.4 +/- 0.7%, 1.9 +/- 0.7%, and 3.3 +/- 0.2%) at 0.5, 1.5, and 4 T, respectively. The signal-to-noise ratio in optimized, fully relaxed proton density weighted gradient echo images was found to increase linearly with respect to the static magnetic field strength (B0). The predicted upper bound on BOLD contrast-to-noise ratio (deltaS/R)max as a function of field strength was calculated and found to behave less than linearly in voxels containing vessels larger than the voxel itself and greater than linearly in voxels containing a mixture of capillaries and veins/venules with a diameter less than that of the voxel.

We investigated the effects of repetition priming on the time course of recognition in several visual areas of the brain using fMRI. We slowed down recognition by gradually revealing the stimuli, in order to prolong the pre-recognition phase. Activation was lower for primed than for non-primed objects overall in both the occipitotemporal region (OTR) and the intraparietal region (IPR). A difference was found between primed and non-primed objects in the rate of increase of OTR activation. We concluded that the IPR, in addition to the OTR, was affected by repetition priming, and that this effect was different from that seen in the OTR.

Social cognition is a dynamic process that requires the perception and integration of a complex set of idiosyncratic features between interacting conspecifics. Here we present a method for simultaneously measuring the whole-brain activation of two socially interacting marmoset monkeys using functional magnetic resonance imaging. MRI hardware (a radiofrequency coil and peripheral devices) and image-processing pipelines were developed to assess brain responses to socialization, both on an intra-brain and inter-brain level. Notably, brain-activation maps acquired during constant interaction demonstrated neuronal synchrony between marmosets in regions of the brain responsible for processing social interaction. This method enables a wide range of possibilities for studying social function and dysfunction in a non-human primate model, including using transgenic models of neuropsychiatric disorders.

Repetitive transcranial magnetic stimulation (rTMS), when applied to left dorsolateral prefrontal cortex (LDLPFC), reduces negative symptoms of schizophrenia, but has no effect on positive symptoms. In a small number of cases, it appears to worsen the severity of positive symptoms. It has been hypothesized that high frequency rTMS of the LDLPFC might increase the dopaminergic neurotransmission by driving the activity of the left striatum in the basal ganglia (LSTR) -increasing striatal dopaminergic activity. This hypothesis relies on the assumption that either the frontal-striatal connection or the intrinsic frontal and/or striatal connections covary with the severity of positive symptoms. The current work aimed to evaluate this assumption by studying the association between positive and negative symptoms severity and the effective connectivity within the frontal and striatal network using dynamic causal modeling (DCM) of ultra-high field (7 Tesla) resting state fMRI in a sample of 19 first episode psychosis (FEP) subjects. We found that of all core symptoms of schizophrenia, only delusions are strongly associated with the fronto striatal circuitry. Stronger intrinsic inhibitory tone of LDLPFC and LSTR, as well as a pronounced backward inhibition of the LDLPFC on the LSTR related to the severity of delusions. We interpret that an increase in striatal dopaminergic tone that underlies delusional symptoms, is likely associated with increased prefrontal inhibitory tone, strengthening the frontostriatal 'brake'. Furthermore, based on our model, we propose that lessening of positive symptoms could be achieved by means of continuous theta-burst or low frequency (1Hz) rTMS of the prefrontal area.