Representation of spatial frequency and orientation in the visual cortex

Knowledge of the response of the primary visual cortex to the various spatial frequencies and orientations in the visual scene should help us understand the principles by which the brain recognizes patterns. Current information about the cortical layout of spatial frequency response is still incomplete because of difficulties in recording and interpreting adequate data. Here, we report results from a study of the cat primary visual cortex in which we employed a new image-analysis method that allows improved separation of signal from noise and that we used to examine the neurooptical response of the primary visual cortex to drifting sine gratings over a range of orientations and spatial frequencies. We found that (i) the optical responses to all orientations and spatial frequencies were well approximated by weighted sums of only two pairs of basis pictures, one pair for orientation and a different pair for spatial frequency; (ii) the weightings of the two pictures in each pair were approximately in quadrature (1/4 cycle apart); and (iii) our spatial frequency data revealed a cortical map that continuously assigns different optimal spatial frequency responses to different cortical locations over the entire spatial frequency range.     

Book reviews

JGIM solicits reviews of new books from its readers. If you wish to review a book, please submit a letter of intent that identifies the book in question (title, author, and publisher) to Robert Aronowitz, MD, Book Review Editor,JGIM, Department of Medicine, Cooper Hospital, 3 Cooper Plaza—Suite 220, Camden, NJ 08103, telephone (609)342-2489.     

Use of a mouth gag instrument to facilitate bite block insertion and prevent finger and probe bites during transesophageal echocardiography

Transesophageal echocardiography greatly enhances the examination of patients difficult to image transthoracically. While of low patient risk, a potential for harm from human bites to the echocardiography staff and to the transesophageal probe remains, particularly when dealing with uncooperative patients. This risk potential prompted implementation of additional anti-bite protection in our universal precautions policy beyond use of a standard mouth guard. A mouth gag instrument was modified by placing latex rubber tubing over the instrument blades. This instrument was inserted into the mouth and set in an open position giving the operator safe access for probe and mouth bite guard insertion. This technique improved access to the patient's mouth and visualization of probe insertion without the mouth bite guard. The mouth gag instrument provided an insertion of the transesophageal probe in impaired or otherwise uncooperative patients, which was safer for the patient, laboratory staff, and the probe itself.     

Relationship of HLA to schizophrenia not supported in multiplex families.

The role of the human histocompatibility complex (HLA) in the pathogenesis of schizophrenia has been suggested in previous reports. We conducted a genetic study in 33 new families. Our linkage analysis, which used the affected sib-pair method, did not provide evidence for nonrandom assortment. Moreover, the results of an association study using the "haplotype relative risk" method failed to confirm the positive association between HLA A9 and schizophrenia. Taken together, our data did not support any relationship of HLA type to schizophrenia.     

The reconstitution of cell-mediated immunity in the cutaneous lesions of lepromatous leprosy by recombinant interleukin 2

Human rIL-2 (10-30 micrograms) was injected intradermally into the skin of patients with lepromatous leprosy with high bacillary loads. All patients responded to the lymphokine with local areas of induration that peaked at 24 h and persisted for 4-7 d irrespective of whether the site was "normal skin" or a nodular lesion. Within 24 h there was an extensive emigration of T cells and monocytes into the site. The percentage of the dermis infiltrated by mononuclear cells increased by more than sevenfold, peaking at 4 d and persisting for greater than 15 d. Both CD4+ and CD8+ T cells entered the site. T cells of CD4+ phenotype predominated at 2-7 d but by 11 d, CD8+ cells were predominant. Considerable numbers of T6+ Langerhans' cells appeared in the dermis by 72 h and persisted for 3 wk. By 4 d the thickness of the overlying epidermis had increased twofold, and keratinocytes were expressing MHC class II antigen and the IFN-gamma-induced peptide IP-10. Starting at 48 h, there was an extensive destruction of mononuclear phagocytes that contained structurally intact or fragmented M. leprae observed at the electron microscope level. The organisms, either free or contained within endocytic vacuoles, were discharged into the extracellular space and then reingested by blood-borne monocytes. This was followed by marked reductions in the number of acid-fast organisms in the injected site, evident as early as 4-7 d and more marked at 2-3 wk after injection. 13 of 15 patients exhibited a disposal of acid-fast bacilli ranging from 5- to 1,000-fold with a mean value of approximately 100-fold. The administration of IL-2 leads to the generation of an effective cell-mediated immune response, recapitulating an antigen-driven event and leading to striking local reductions in M. leprae. In comparison with the purified protein derivative of tuberculin reaction, bacilli are cleared more promptly, although emigratory cells persist for a shorter time.