Neural dynamics in a model of the thalamocortical system. I. Layers, loops and the emergence of fast synchronous rhythms

A large-scale computer model was constructed to gain insight into the structural basis for the generation of fast synchronous rhythms (20-60 Hz) in the thalamocortical system. The model consisted of 65,000 spiking neurons organized topographically to represent sectors of a primary and secondary area of mammalian visual cortex, and two associated regions of the dorsal thalamus and the thalamic reticular nucleus. Cortical neurons, both excitatory and inhibitory, were organized in supragranular layers, infraganular layers and layer IV. Reciprocal intra- and interlaminar, interareal, thalamocortical, corticothalamic and thalamoreticular connections were set up based on known anatomical constraints. Simulations of neuronal responses to visual input revealed sporadic epochs of synchronous oscillations involving all levels of the model, similar to the fast rhythms recorded in vivo. By systematically modifying physiological and structural parameters in the model, specific network properties were found to play a major role in the generation of this rhythmic activity. For example, fast synchronous rhythms could be sustained autonomously by lateral and interlaminar interactions within and among local cortical circuits. In addition, these oscillations were propagated to the thalamus and amplified by corticothalamocortical loops, including the thalamic reticular complex. Finally, synchronous oscillations were differentially affected by lesioning forward and backward interareal connections.      

Epstein-Barr virus genomes are restricted to secondary neoplastic cells following bone marrow transplantation

DNA from mononuclear blood and tumor cells from 33 patients undergoing bone marrow transplantation for leukemia was examined for the presence of Epstein-Barr virus (EBV) genomes by blot hybridization. Four groups of patients were studied soon after engraftment, during long-term remission, after relapse of the original leukemia, and after development of secondary B cell neoplasms. Only the cells of patients with secondary neoplasms demonstrated EBV genomes, where all five adequately studied samples were positive. Samples from all other patient categories were negative for EBV genomes. We conclude that EBV genomes do not frequently persist in normal engrafted lymphocytes or in mononuclear cells of patients suffering recurrent leukemia. These results are consistent with EBV playing a role in the genesis of secondary B cell neoplasms following bone marrow transplantation.     

Transfusion-transmitted babesiosis: a case report from a new endemic area

The seventh documented case of babesiosis transmitted by transfusion is reported. Both the donor and the recipient are residents of Connecticut, where the presence of endemic babesiosis has only recently been established. As the range of Babesia microti, and its vector the Ixodes dammini tick, continues to expand, clinicians and blood bank directors should be aware that cases of transfusion-transmitted babesiosis may occur in newly endemic areas.     

Marrow transplantation for patients with acute lymphoblastic leukemia: a long-term follow-up

Twenty-two patients with acute lymphoblastic leukemia in second or subsequent remission and 26 with acute lymphoblastic leukemia in relapse were given cyclophosphamide (60 mg/kg on each of 2 days), total body irradiation (920 rad), and marrow transplants from HLA-identical siblings. With a minimum follow-up of more than 5 yr, an actuarial analysis shows a survival and apparent cure of 27% of the patients transplanted in remission and 15% of the patients transplanted in relapse.