The active pulley hypothesis proposes that the orbital layers (OLs) of rectus EOMs translate their connective tissue pulleys, while the global layers (GLs) rotate the eye. Rectus pulleys are actively controlled so that EOM velocity vectors shift by half the change in eye orientation, implementing a linear ocular motor plant. To evaluate the oblique EOM contribution, magnetic resonance imaging (MRI) of EOM paths was performed in humans, and correlated with histologic examination of 9 human (ages 0 – 93 yrs) and 8 monkey (rhesus, fascicularis, nemestrina, cebus) orbits. In all species, the inferior oblique (IO) muscle OL inserted on its collagenous pulley that was contiguous with the inferior rectus (IR) pulley, and on the lateral rectus (LR) pulley. This forces the IO to be coplanar with the IR and LR pulleys, and permits the contracting IO to displace both the IR and LR pulleys as verified by MRI. MRI shows IR contraction to displace the IO pulley by half the travel of the IR insertion. Mechanical coupling...

The ability to switch from one task to another is central to intelligent behavior, as it allows an organism to cope efficiently with the demands of swiftly changing environments. Human functional magnetic resonance imaging (fMRI) studies have indicated ...

The medial temporal lobe (MTL) is essential for episodic memory encoding, as evidenced by memory deficits in patients with MTL damage. However, previous functional neuroimaging studies have either failed to show MTL activation during encoding or they did not differentiate between two MTL related processes: novelty assessment and episodic memory encoding. Furthermore, there is evidence that the MTL can be subdivided into subcomponents serving different memory processes, but the extent of this functional subdivision remains unknown. The aim of the present functional magnetic resonance imaging (fMRI) study was to investigate the role of the MTL in episodic encoding and to determine whether this function might be restricted to anatomical subdivisions of the MTL. Thirteen healthy volunteers performed a word list learning paradigm with free recall after distraction. Functional images acquired during encoding were analyzed separately for each participant by a voxel-wise correlation (Kendall’s tau) between the tim...

The brightness and color of a surface depends on its contrast with nearby surfaces. For example, a gray surface can appear very light when surrounded by a black surface or dark when surrounded by a white surface. Some theories suggest that perceived surface brightness and color is represented explicitly by neural signals in cortical visual field maps; these neural signals are not initiated by the stimulus itself but rather by the contrast signals at the borders. Here, we use functional magnetic resonance imaging (fMRI) to search for such neural “filling-in” signals. Although we find the usual strong relationship between local contrast and fMRI response, when perceived brightness or color changes are induced by modulating a surrounding field, rather than the surface itself, we find there is no corresponding local modulation in primary visual cortex or other nearby retinotopic maps. Moreover, when we model the obtained fMRI responses, we find strong evidence for contributions of both local and long-range edg...

Therapeutic success of treatment of cerebral diseases must be assessed in terms of functional outcome. In experimental stroke studies, this has been limited to behavioral studies combined with morphological evaluations and single time point functional magnetic resonance imaging (fMRI) measurements but lacking the access to understanding underlying mechanisms for alterations in brain activation. Using a recently developed blood oxygenation level-dependent fMRI protocol to study longitudinal and intraindividual profiles of functional brain activation in the somatosensory system, we have demonstrated activation reemergence in the original representation field as the basic principle of functional recovery from experimental stroke. No plastic reorganization has been observed at any time point during 7 weeks after stroke induction. Applying combined recording of fMRI and somatosensory evoked potentials, we observed a tight coupling of electrical brain activity and hemodynamic response at all times, indicating pe...

We have examined the activity levels produced in various areas of the human occipital cortex in response to various motion stimuli using functional magnetic resonance imaging (fMRI) methods. In addition to standard luminance-defined (first-order) motion, three types of second-order motion were used. The areas examined were the motion area V5 (MT) and the following areas that were delineated using retinotopic mapping procedures: V1, V2, V3, VP, V3A, and a new area that we refer to as V3B. Area V5 is strongly activated by second-order as well as by first-order motion. This activation is highly motion-specific. Areas V1 and V2 give good responses to all motion stimuli, but the activity seems to be related primarily to the local spatial and temporal structure in the image rather than to motion processing. Area V3 and its ventral counterpart VP also respond well to all our stimuli and show a slightly greater degree of motion specificity than do V1 and V2. Unlike V1 and V2, the response in V3 and VP is significa...

In this study we were interested in the hypothesis that different task sets would influence both behavior and prefrontal cortex (PFC) activation during performance of a memory task. Specifically, participants were asked to remember a list of words over a short delay, and then respond to a probe word, indicating whether or not the probe was present in the list of words. In one condition, participants were encouraged to use an active maintenance strategy by presenting short lists of words (1 to 6 words per list). In the other condition, participants were encouraged to use a retrieval-based strategy by presenting long lists of words (6 to 11 words per list). The critical comparison is between the 6-word trials, since the memory load, trial duration, and perceptual input are identical across the two conditions. To test our hypothesis that activation in PFC would correlate with task set, we conducted an event-related functional magnetic resonance imaging (fMRI) study on 25 younger adults. Behavioral results con...

Functional magnetic resonance imaging (fMRI) was used to monitor spinal cord mediated activation of sensory motor cortex by measuring changes of blood oxygenation level-dependent (BOLD) contrast during electric stimulation of forepaw, hindpaw or tail. Single or multi-slice gradient echo images were collected using gradient echo fast imaging or spiral gradient imaging. Stimulation of fore- or hindpaws repeatedly lead to robust activation of contralateral sensorimotor cortex. The center of the main cortical representation was situated 3.4 mm lateral to the midline and 5 mm posterior to the rhinal fissure (prf) for the forepaw and 2.0 mm lateral to the midline and 6 mm prf for the hindpaw. Tail stimulation gave rise to an extended bilateral cortical activation, along the midline in medial frontal and cingulate gyrus 4 and 5 mm prf. Axonal regeneration in peripheral nerves has been obtained using degradable tubes made of polyglycolic acid (PGA) and collagen (Kiyotani et al., 1996 Brain Res, 740:66-74). To obta...

Experimental data up to 7.0 T show that the blood oxygenation level-dependent (BOLD) signal of functional magnetic resonance imaging (fMRI) increases with higher magnetic field strength. Although several studies at 11.7 T report higher BOLD signal compared with studies at 7.0 T, no direct comparison at these two field strengths has been performed under the exact same conditions. It therefore remains unclear whether the expected increase of BOLD effect with field strength will still continue to hold for fields >7.0 T. To examine this issue, we compared the BOLD activation signal at 7.0 and 11.7 T with the two common sequences, spin-echo (SE) and gradient-echo (GE) echo planar imaging (EPI). We chose the physiologically well controlled rat model of electrical forepaw stimulation under medetomidine sedation. While a linear to superlinear increase in activation with field strengths up to 7.0 T was reported in the literature, we observed no significant activation difference between 7.0 and 11.7 T with either SE...

Correction: In the article “A Comparative Magnetic Resonance Imaging Study of the Anatomy, Variability, and Asymmetry of Broca's Area in the Human and Chimpanzee Brain” by Simon S. Keller, Neil Roberts, and William Hopkins, which appeared on pages [14607–14616][1] of the November 18, 2009