Distributed and overlapping representations of faces and objects in ventral temporal cortex.

The functional architecture of the object vision pathway in the human brain was investigated using functional magnetic resonance imaging to measure patterns of response in ventral temporal cortex while subjects viewed faces, cats, five categories of man-made objects, and nonsense pictures. A distinct pattern of response was found for each stimulus category. The distinctiveness of the response to a given category was not due simply to the regions that responded maximally to that category, because the category being viewed also could be identified on the basis of the pattern of response when those regions were excluded from the analysis. Patterns of response that discriminated among all categories were found even within cortical regions that responded maximally to only one category. These results indicate that the representations of faces and objects in ventral temporal cortex are widely distributed and overlapping.

Melatonin hypersecretion in male patients with adult-onset idiopathic hypogonadotropic hypogonadism.

Increased melatonin secretion observed in male patients with congenital isolated hypogonadotropic hypogonadism and its normalization during testosterone treatment had suggested that melatonin and the reproductive hormones are inter-related. Since these patients have a congenital form of hypogonadism, it is likely that hypermelatoninemia is the consequence of hypogonadism. To further study the relations between the pineal and the reproductive axis in humans, we evaluated melatonin secretion in two men (aged 35 and 50 yrs.) with acquired adult-onset hypogonadotropic hypogonadism. The diagnosis was based on the findings of normal testicular volume, azoospermia, low serum testosterone, normal LH and FSH levels, but apulsatile LH secretion, and intact anterior pituitary hormones secretion, normal findings on skull radiographic imaging, prior sexual maturation and paternity. Melatonin secretion was assessed as urinary 24 h 6-sulphatoxymelatonin excretion (aMT6s) prior to and during the administration of 250 mg testosterone enanthate per month for 4 months. Pretreatment melatonin production was markedly increased in both patients: 427-915 ng/kg/24 h vs. 204+/-81 [mean+/-SD] in 16 age-matched male controls. During testosterone treatment, aMT6s levels were normalized in one patient (range: 81-287 ng/kg/24 h) and remained elevated in the other patient (range: 830-1280 ng/kg/24 h). These data indicate that male patients with acquired GnRH deficiency have increased melatonin secretion. Melatonin hypersecretion in these patients may reflect a functional association.

Distributed neural systems for the generation of visual images.

Visual perception of houses, faces, and chairs evoke differential responses in ventral temporal cortex. Using fMRI, we compared activations evoked by perception and imagery of these object categories. We found content-related activation during imagery in extrastriate cortex, but this activity was restricted to small subsets of the regions that showed category-related activation during perception. Within ventral temporal cortex, activation during imagery evoked stronger responses on the left whereas perception evoked stronger responses on the right. Additionally, visual imagery evoked activity in parietal and frontal cortex, but this activity was not content related. These results suggest that content-related activation during imagery in visual extrastriate cortex may be implemented by "top-down" mechanisms in parietal and frontal cortex that mediate the retrieval of face and object representations from long-term memory and their maintenance through visual imagery.

The representation of objects in the human occipital and temporal cortex.

Recently, we identified, using fMRI, three bilateral regions in the ventral temporal cortex that responded preferentially to faces, houses, and chairs [Ishai, A., Ungerleider, L. G., Martin, A., Schouten, J. L., & Haxby, J. V. (1999). Distributed representation of objects in the human ventral visual pathway. Proceedings of the National Academy of Sciences, U.S.A., 96, 9379--9384]. Here, we report differential patterns of activation, similar to those seen in the ventral temporal cortex, in bilateral regions of the ventral occipital cortex. We also found category-related responses in the dorsal occipital cortex and in the superior temporal sulcus. Moreover, rather than activating discrete, segregated areas, each category was associated with its own differential pattern of response across a broad expanse of cortex. The distributed patterns of response were similar across tasks (passive viewing, delayed matching) and presentation formats (photographs, line drawings). We propose that the representation of objects in the ventral visual pathway, including both occipital and temporal regions, is not restricted to small, highly selective patches of cortex but, instead, is a distributed representation of information about object form. Within this distributed system, the representation of faces appears to be less extensive as compared to the representations of nonface objects.

Distributed representation of objects in the human ventral visual pathway.

Brain imaging and electrophysiological recording studies in humans have reported discrete cortical regions in posterior ventral temporal cortex that respond preferentially to faces, buildings, and letters. These findings suggest a category-specific anatomically segregated modular organization of the object vision pathway. Here we present data from a functional MRI study in which we found three distinct regions of ventral temporal cortex that responded preferentially to faces and two categories of other objects, namely houses and chairs, and had a highly consistent topological arrangement. Although the data could be interpreted as evidence for separate modules, we found that each category also evoked significant responses in the regions that responded maximally to other stimuli. Moreover, each category was associated with its own differential pattern of response across ventral temporal cortex. These results indicate that the representation of an object is not restricted to a region that responds maximally to that object, but rather is distributed across a broader expanse of cortex. We propose that the functional architecture of the ventral visual pathway is not a mosaic of category-specific modules but instead is a continuous representation of information about object form that has a highly consistent and orderly topological arrangement.

Transient cold nodule of the thyroid due to localized postpartum thyroiditis.

A 27-year-old woman with no previous personal or family history of thyroid disease was referred to us for the evaluation of thyroid nodule, five months postpartum. Thyroid scintigraphy demonstrated a left cold nodule. Fine needle aspiration cytology of the nodule showed a mixture of colloid, follicular cells and lymphocytes, suggesting lymphocytic thyroiditis. Thyroid function tests were normal and thyroid autoantibodies were negative. After two months the thyroid nodule was not palpated and thyroid scintigraphy returned to normal. Thyroid function tests remained normal twelve months after delivery. These findings suggest that postpartum thyroiditis may present as a localized transient form and should be considered in the differential diagnosis of painless solitary nodule that appears postpartum.

Visual imagery: effects of short- and long-term memory.

Visual imagery and perception share several functional properties and apparently share common underlying brain structures. A main approach to the scientific study of visual imagery is exploring the effects of mental imagery on perceptual processes. Previous studies have shown that visual imagery interferes with perception (Perky effect). Recently we have shown a direct facilitatory effect of visual imagery on visual perception. In an attempt to differentiate the conditions under which visual imagery interferes or facilitates visual perception, we designed new experimental paradigms, using detection tasks of a Gabor target. We found that imagery-induced interference and facilitation are memorydependent: Visual recall of common objects from long-term memory can interfere with perception, while on short-term memory tasks facilitation can be obtained. These results support the distinction between low-level and structural representations in visual memory.

Visual imagery facilitates visual perception: psychophysical evidence.

Visual imagery is the invention or recreation of a perceptual experience in the absence of retinal input.The degree to which the same neural representations are involved in both visual imagery and visual perception is unclear. Previous studies have shown that visual imagery interferes with perception (Perky effect). We report here psychophysical data showing a direct facilitatory effect of visual imagery on visual perception. Using a lateral masking detection paradigm of a Gabor target, flanked by peripheral Gabor masks, observers performed imagery tasks that were preceded by perceptual tasks. We found that both perceived and imaginary flanking masks can reduce contrast detection threshold. At short target-to-mask distances imagery induced a threshold reduction of 50% as compared with perception, while at long target-to-mask distances imagery and perception had similar facilitatory effect. The imagery-induced facilitation was specific to the orientation of the stimulus, as well as to the eye used in the task. These data indicate the existence of a stimulus-specific short-term memory system that stores the sensory trace and enables reactivation of quasi-pictorial representations by topdown processes. We suggest that stimulus parameters dominate the imagery-induced facilitation at short target-to-mask distances, yet the topdown component contributes to the effect at long target-to-mask distances.

Thyromimetic mode of action of peroxisome proliferators: activation of 'malic' enzyme gene transcription.

Peroxisome proliferators induce thyroid-hormone-dependent liver activities, e.g. 'malic' enzyme, mitochondrial glycerol-3-phosphate dehydrogenase, glucose-6-phosphate dehydrogenase, S14[Hertz, Aurbach, Hashimoto and Bar-Tana (1991) Biochem. J. 274, 745-751]. Here we report that the thyromimetic effect of peroxisome proliferators with respect to 'malic' enzyme result from transcriptional activation of the 'malic' enzyme gene, mediated by binding of the peroxisome proliferator activated receptor (PPAR alpha)/retinoid X receptor (RXR alpha) heterodimer to a 5'-flanking enhancer of the 'malic' enzyme promoter. The enhancer involved is distinct from the thyroid hormone response element of the 'malic' enzyme promoter and is partly homologous with that which mediates transcriptional activation of peroxisomal acyl-CoA oxidase by peroxisome proliferators. Hence transcriptional activation of thyroid-hormone-dependent liver genes by xenobiotic or endogenous amphipathic carboxylates collectively defined as peroxisome proliferators is mediated by a transduction pathway similar to that involved in transcriptional activation of peroxisomal beta-oxidative genes and distinct from that which mediates thyroid hormone action.

Common mechanisms of visual imagery and perception.

Detection of a visual target can be facilitated by flanking visual masks. A similar enhancement in detection thresholds was obtained when observers imagined the previously perceived masks. Imagery-induced facilitation was detected for as long as 5 minutes after observation of the masks by the targeted eye. These results indicated the existence of a low-level (monocular) memory that stores the sensory trace for several minutes and enables reactivation of early representations by higher processes. This memory, with its iconic nature, may subserve the interface between mental images and percepts.