Although a large number of categories and category classes represented along the ventral stream have been found in the human visual system, it has been difficult to outline the anatomical circuitry underlying the receptive field properties of object selective neurons due to the lack of non-invasive techniques. Here, the relationship between functional activity and neuronal connectivity across the striate and extrastriate cortical areas were investigated. Neuronal connections between areas of different receptive field properties were assessed in vivo using the Diffusion Tensor Magnetic Resonance Imaging (DT-MRI) in combination with functional magnetic resonance imaging (fMRI). DTI in conjunction with functional MRI was performed using a 3 Tesla whole body scanner (Trio, Siemens). Functional imaging scans were used to localize retinotopic and non-retinotopic visual areas in healthy human volunteers. BOLD contrast was obtained using gradient-echo echo-planar imaging (EPI) sequence (30 axial slices of 2-mm thi...

Sensory processing deficits in schizophrenia have been documented for several decades, but their underlying neurophysiological substrates are still poorly understood. In the visual system, the pattern of pathophysiology reported in several studies is suggestive of dysfunction within the magnocellular visual pathway beginning in early sensory cortex or even subcortically. The present study used functional magnetic resonance imaging to investigate further the neurophysiological bases of visual processing deficits in schizophrenia and in particular the potential role of magnocellular stream dysfunction. Sinusoidal gratings systematically varying in spatial frequency content were presented to subjects at low and high levels of contrast to differentially bias activity in magnocellular and parvocellular pathways based on well established differences in neuronal response profiles. Hemodynamic responses elicited by different spatial frequencies were mapped over the occipital lobe and then over the entire brain. Re...

A great deal is known about the response properties of single neurons processing sensory information. In contrast, less is understood about the collective characteristics of networks of neurons that may underlie sensory capacities of animals. We used functional magnetic resonance imaging to study the emergent properties of populations of neurons processing motion across different brain areas. Using a visual adaptation paradigm, we localized a distributed network of visual areas that process information about the direction of motion as expected from single-cell recording studies. However, we found an apparent discrepancy between the directional signals in certain visual areas as measured with blood oxygenation level-dependent imaging compared with an estimate based on the spiking of single neurons. We propose a hypothesis that may account for this difference based on the postulate that neuronal selectivity is a function of the state of adaptation. Consequently, neurons classically thought to lack informatio...

As it is the case worldwide, marijuana (cannabis) use in the United States and Canada is highly prevalent and societal views of its use are changing rapidly, as are the policies that govern the legality of its recreational and medical use. With the rece...

The feasibility of non-invasive imaging of neuronal currents (NCI) in the brain by means of Nuclear Magnetic Resonance (NMR) techniques has been debated for more than a decade. NCI cannot be easily applied at high Larmor fields (>1T) due to (i) the rela...

Most blood-oxygen level dependent functional magnetic resonance imaging (BOLD-fMRI) protocols measure neuronal activity under anaesthesia. Alpha-chloralose is the agent most frequently used for this. However, side-effects including acidosis and involunt...

Although neuropsychological studies of the amnesic patient H. M. provide compelling evidence that normal memory function depends on the medial temporal lobe, the full extent of his surgical resection has not been elucidated. We conducted magnetic resonance imaging studies to specify precisely the extent of his bilateral resection and to document any other brain abnormalities. The MRI studies indicated that the lesion was bilaterally symmetrical and included the medial temporal polar cortex, most of the amygdaloid complex, most or all of the entorhinal cortex, and approximately half of the rostrocaudal extent of the intraventricular portion of the hippocampal formation (dentate gyrus, hippocampus, and subicular complex). The collateral sulcus was visible throughout much of the temporal lobe, indicating that portions of the ventral perirhinal cortex, located on the banks of the sulcus, were spared; the parahippocampal cortex (areas TF and TH) was largely intact. The rostrocaudal extent of the ablation was ∼5...

In the article “Magnocellular Pathway Impairment in Schizophrenia: Evidence from Functional Magnetic Resonance Imaging” by Antígona Martínez, Steven A. Hillyard, Elisa C. Dias, Donald J. Hagler Jr, Pamela D. Butler, David N. Guilfoyle, Maria Jalbrzikowski, Gail Silipo, and Daniel C. Javitt,

The lateral geniculate nucleus (LGN) is a key subcortical brain structure of the human visual system. Traditionally, non-invasive spatial mapping of the LGN proved challenging due to its small size and deep position within the brain. However, recent adv...

Learning is thought to facilitate the recognition of objects by optimizing the tuning of visual neurons to behaviorally relevant features. However, the learning mechanisms that shape neural selectivity for visual forms in the human brain remain essentially unknown. Here, we combine behavioral and functional magnetic resonance imaging (fMRI) measurements to test the mechanisms that mediate enhanced behavioral sensitivity in the discrimination of visual forms after training. In particular, we used high-resolution fMRI and multivoxel pattern classification methods to investigate fine learning-dependent changes in neural preference for global forms. We measured the observers' choices when discriminating between concentric and radial patterns presented in noise before and after training. Similarly, we measured the choices of a pattern classifier when predicting each stimulus from fMRI activity. Comparing the performance of human observers and classifiers demonstrated that learning alters the observers' sensitiv...