Converging lines of evidence suggest that the Human Immunodeficiency Virus (HIV) can cause frontal-subcortical damage and cognitive dysfunction. Neuropsychological studies have demonstrated sensitivity of the Stroop Interference Task to HIV-related cognitive dysfunction, but the underlying pathophysiology is poorly understood. In this study, fMRI (1.5T Siemens, TR=2, 21 slices of 5 mm, blocked design, SPM '99) was used to compare patterns of brain activity in 9 HIV-positive (HIV+) and 8 HIV-negative (HIV-) males during performance of two Stroop-variant tasks. In the Counting Stroop (Bush '98), subjects used a button-press to indicate the number of animal names (neutral) or incongruent number words (interference) presented on a screen. HIV+ subjects were slower and more susceptible to interference than HIV- subjects. FMRI analysis (interference vs. neutral) showed that HIV+ subjects also recruited more regions of motor and parietal cortex compared to HIV- subjects. In the Oddball Stroop (Bush, personal comm...

Transgenic mouse models of Alzheimer’s disease are produced to understand the role of particular genes and to have available animal models, which mimic the clinical condition in order to test therapeutic interventions. Thus, there is a growing need for non-invasive tracking of pathology in mice at high spatial resolutions, afforded by high-resolution MRI (microMRI). - In this study we used microMRI to follow structural changes over 2 years in brains of transgenic mice overexpressing V717F APP (PDAPP mice). Homozygous (n=11), heterozygous (n=8) PDAPP female mice and wildtype controls (n=7) initially 3-6 months of age were used for the study. The mice were imaged every three months for 22 months. All imaging was performed on a 7.1 T magnet using a 3D diffusion-weighted sequence and a spatial resolution of 58 µm x 58 µm x 469 µm. Quantitative analysis of was performed using NIH image. The most striking structural difference between homozygous PDAPP mice and wildtype mice was the magnitude of lateral and 3rd v...

We used event-related functional magnetic resonance imaging (fMRI) to examine activations of the distributed neural systems for the oculomotor control in awake macaque monkeys. The monkeys (macaca fuscata) were trained to perform fixation and saccade tasks in a 1.5T or 4.7T MRI scanner. The eye positions of the animals were monitored with an infrared-sensitive CCD camera. During fMRI session, the fixation trial and saccade trial were pseudorandomly interleaved. On fixation trials, the animals must keep fixation within 1.5 degree of the central spot. On saccade trials, they were required to make saccade to one of the eight peripheral positions at the eccentricity of ten degrees (Fukushima et al, Soc. Neurosci. Abstr. 2000). Standard T2*-weighted echo-planar imaging protocols (Hayashi et al. Eur. J. Neurosci. 1999) were used to obtain the blood oxygenation level-dependent signal. The time series data were analyzed with SPM99, assigning event-related contrasts for different types of trials. We found focal act...

Muscles that would be predicted to have the same functions may have different functions when examined in detail. For example, the lateral gastrocnemius (LG) and medial gastrocnemius (MG) muscles appear to be differentially activated during turning while walking and also during unilateral heel raises.To further examine the relative activity of leg muscles we compared the activity of muscles used during unilateral heel raises versus bilateral heel raises using T2 weighted MR images. Subjects were scanned prior to and after performing 60-100 s of bilateral and/or unilateral heel raises at a rate of 1 per 2 s. There was at least a 40 minute rest period between exercise epochs. For both bilateral and unilateral heel raises, whether analyzing whole muscles or if the muscles are divided into proximal, middle and distal portions, the peroneal (PER) muscles are the most active. Typically, MG is next most active followed by LG. The soleus (SOL) is not very active during bilateral heel raises, but increases to levels...

It is still unclear to what extent cortical areas are involved in non-conscious processing of tactile stimuli. However, from subdural recordings of somatosensory evoked potentials in awake humans there is evidence for excitation of areas in the postcentral gyrus in response to peripheral subliminal electrical stimulation without any associated conscious sensation (Libet et al. 1967). For further investigation an fMRI study (6 subjects, mean age±S.D.=27.7±2.3 yrs) was performed with an 1.5 T scanner using echoplanar sequences (TR=2 s, FOV=256 mm, voxel size=4×4×5 mm, 16 slices). Blocks (10 scans) of subthreshold and suprathreshold electrical stimuli (pulse frequency=7 Hz, pulse duration=0.2 ms), at least 15% below (2.2±0.42 mA) and 15% above (3.1±0.62 mA) sensory threshold for conscious perception (2.7±0.52 mA), respectively, were scan triggered and delivered in a randomized order to the left index finger via ring electrodes. Parametrical maps were calculated using BrainVoyager. In the group analysis, subth...

Previous functional neuroimaging studies have not determined cortical areas of selective somatosensory processing of stimulus attributes or location. To address this, we studied 20 subjects trained in two tactile tasks. For both tasks, a set of domes with gratings was used. Gratings were delivered to the immobilized finger. For each trial, a grating was first applied distally with the bars/grooves parallel to the long axis of the finger. Subjects were either required to judge if the grating orientation (GOT) or stimulation site (location task (LOT) changed during a 2nd presentation. Subjects attended to either orientation or location while activations were measured using block design fMRI at 3T. Group performance was very similar for the GOT (74% correct responses) and LOT (74%). Similar activations for both tasks were seen in the primary and secondary somatosensory cortices. The intraparietal sulcus (IPS) was preferentially activated bilaterally in most subjects during the GOT. However, there were signifi...

The capacity to attend to task demands while viewing nontask-related emotional stimuli undergoes profound development during adolescence. However, researchers are only beginning to explore neurobiological correlates of this cognitive process. In the present investigation, 17 adolescents (9-17 years of age) and 17 adults (25-36 years of age) were scanned using event-related fMRI at 3T. Subjects viewed neutral and emotional faces (angry, fearful and happy) passively and also while attending to emotional and physical features. In the initial analysis, three main results emerged. (1) Adolescents showed greater amygdala and prefrontal cortex activation than adults during passive viewing of angry vs. neutral faces. (2) Both adults and adolescents engaged ventral lateral and dorsal prefrontal regions while attending to internal fear state during angry vs neutral face viewing. (3) Greater discriminant activation emerged in adults vs. adolescents within the contrast of internal fear rating to angry faces vs. physic...

The present study evaluates the contribution of the thalamus to cognition using structural MRI-based volumetry in combination with neurocognitive testing of healthy subjects, Korsakoff's (KS) and Alzheimer's (AD) patients. Fifty-seven healthy subjects ranging from 21 to 82 years old were included. It could be shown that a highly significant decrease in thalamic volume occurred with higher age, stronger than and independent of total brain volume (r=-0.599, p=0.000). In young, but not in middle-aged or old subjects, thalamic volume was related to speeded information processing. This was evident from performance on the Stroop test, a memory scanning task and a variant of the trail making task. No relationship was found with higher cognitive functions such as semantic or episodic memory. Thalamic volumes of KS patients were smaller than those of healthy controls and non-KS alcoholics. Similarly, AD patients showed reductions in thalamic volume as compared to both healthy subjects and age-associated cognitive d...

Transient fetal subplate zone (SP) consists of loosely arranged axons, postmigratory and migratory neurons, growth cones, synapses and glia (Kostovic & Rakic, J Comp Neurol 297:441, 1990). The developmental peak of SP occurs during the sequential ingrowth of major cortical afferent fibre systems when SP serves as a waiting compartment. To explore the potential of MRI technique for in vivo imaging of the SP, we correlated MR images of postmortem fetal brains with variously stained histological sections of age-matched brains. On Tlw MR images (2T Prestige), the SP is clearly delineated as a zone of low signal intensity, situated between the cortical plate and external axonal stratum. This low intensity probably reflects special biochemical and cytological features of the SP, i.e., its high water content, large extracellular space, and fibrillar structure. The SP appears around 15 weeks of gestation (WG), becomes extensive at 22 WG and expands further until 30 WG, when its resolution begins in depth of cortic...

Our functional MRI studies of complex finger movements in normal subjects have demonstrated two distinct loci of activity on the anterior bank of the central sulcus in primary motor cortex (M1). The first site is located on the knob formed by the inter-digitation of M1 and primary sensory cortex (S1), and the second is found lateral to this knob. The question then arises as to whether these functionally distinct areas share the same neuroanatomical features and whether or not both are part of M1. In order to relate our functional observations to the cyto- and chemoarchitecture of these areas, we imaged (T1-weighted MRI) post-mortem tissue and then performed basic neuroanatomy with Nissl histochemistry and immunohistochemistry for calcium binding proteins (calbindinD28 and parvalbumin) and a non-phosphorylated neurofilament protein (SMI-32). While brain activation in the medial location was clearly embedded in M1, the lateral site was difficult to assess cyto- and chemoarchitectonically. This was due to a d...