The functional significance of mu rhythms: Translating “seeing” and “hearing” into “doing”

Existing evidence indicates that mu and other alpha-like rhythms are independent phenomena because of differences in source generation, sensitivity to sensory events, bilateral coherence, frequency, and power. Although mu suppression and enhancement echo sensorimotor processing in frontoparietal networks, they are also sensitive to cognitive and affective influences and likely reflect more than an idling brain state. Mu rhythms are present at early stages of human development and in other mammalian species. They exhibit adaptive and dynamically changing properties, including frequency acceleration and posterior-to-anterior shifts in focus. Furthermore, individuals can learn to control mu rhythms volitionally in a very short period of time. This raises questions about the mu rhythm's open neural architecture and ability to respond to cognitive, affective, and motor imagery, implying an even greater developmental and functional role than has previously been ascribed to it. Recent studies have suggested that mu rhythms reflect downstream modulation of motor cortex by prefrontal mirror neurons, i.e., cells that may play a critical role in imitation learning and the ability to understand the actions of others. It is proposed that mu rhythms represent an important information processing function that links perception and action—specifically, the transformation of “seeing” and “hearing” into “doing.” In a broader context, this transformation function results from an entrainment/gating mechanism in which multiple alpha networks (visual-, auditory-, and somatosensory-centered domains), typically producing rhythmic oscillations in a locally independent manner, become coupled and entrained. A global or ‘diffuse and distributed alpha system’ comes into existence when these independent sources of alpha become coherently engaged in transforming perception to action.     

Gap junctions: the “kiss of death” and the “kiss of life”

Cells expressing herpes simplex-thymidine kinase (HSV-tk) can be killed “in vitro” within 5 days of treatment with 20 μM ganciclovir (GCV) and transmit this toxicity to adjacent cells lacking HSV-tk; this phenomenon was termed “bystander effect” or “kiss of death”. On testing a large number of cell lines in vitro, a wide range of sensitivity to GCV-mediated bystander killing has been reported. Although intercellular transfer of GCV metabolites through gap junction channels seems to be a likely mechanism for the “kiss of death”, some studies suggest that other pathways may contribute to induced apoptosis of neighboring cells. To further investigate the mechanism underlying cell death mediated by HSV-tk and to evaluate the efficacy of gap junction channels formed by different connexins in this process, we have stably transfected a virtually uncoupled mouse neuroblastoma cell line (N2A cells) with different connexin-types expressed by neural cells (Cx32, Cx37, Cx40, Cx43) and co-cultured these cells with N2A cells stably transfected with Cx37 and HSV-tk. Here, we confirm our previous studies and those of others that the extent of cell death and sensitivity to GCV depend on the degree of connexin expression in transfectants. Further, we show that the bystander effect also depends on which connexin is expressed; reported disparities regarding the extent of GCV-mediated cellular apoptosis are likely due both to the degree of functional coupling and the type of connexin expressed. These results support the notion that gap junction hemichannels formed of certain connexins are more likely than others to pair functionally with Cx37, and suggest co-transfection strategies that might prove effective in sensitizing tumor cell populations to GCV. In addition, potential applications are discussed for use of the “good Samaritan effect”, a mechanism by which bystander cells have been suggested to prevent cytotoxicity.     

“Recumbent” gait: Relationship to the phenotype of “astasia‐abasia”?

Psychogenic gait disorders can present in many different ways. Among patients with a pure psychogenic gait disorder, buckling of the knee is the most common feature, followed by astasia-abasia. Here, we describe one such patient with a very unusual gait disturbance that might be regarded as a variant of astasia-abasia. The patient characteristics are described and discussed in a historical context.     

Perceived social support and dysfunctioning in “clinical” and “normal” adolescents

The purpose of this study was to examine the extent to which inpatient and non-patient samples of youngsters differ from each other with regard to prevalence and co-occurrence of emotional and behavioural problems and negative perceptions of family, school and peers. The sample comprised 202 12–21-year-old adolescents: 101 psychiatric inpatients and 101 matched “community-based” youngsters. Possible differences between the subgroups were tested by means of multi-variate analysis of variance and relative risk ratios.All specific problems and combination patterns were reported significantly more often by the “inpatient” than by the “non-patient” youngsters. However, after correcting for differences in base rates, only the combination of emotional and/or behavioural problems and family problems remained significant. The combination of emotional and family problems was reported about 12 times more often and the combination of behavioural and family problems even about 21 times more often by adolescents in the “clinical” sample than by those in the “normal” sample.Two important conclusions were drawn: (1) co-occurrence in itself did not appear to be the distinguishing factor between the “clinical” and the “normal” sample; and (2) a dominant role of negatively perceived family support in adolescent functioning was suggested. The implications of these findings are discussed.     

A psychological comparison of patients in “open” and “closed” coronary care units

This study demonstrates subtle differences in psychological states of patients in two different coronary care units. In comparing the emotional states and medical course of patients on the two units, the net advantage of the “open unit” seems to be in providing more social contact with associated freedom of expression of hostile feelings, while the lack of privacy resulted in higher levels of “shame anxiety”. The “closed unit”, on the other hand, provided privacy at the expense of human interactions, resulting in increased feelings of loneliness and a displacement of hostile feelings. Certain individual patients may do much better in one or the other type of environment. It is hoped that with further study, it may be possible to identify the characteristics of patients who might be suited to a particular type of C.C.U. Better still, an ideal coronary care unit could be designed, combining the best of both possible worlds, where both “togetherness” and privacy are provided for the patients.

The association found in this and other studies between affective states and the incidence of serious medical complications underline the need to take the patients' emotional welfare into account in the design and staffing of the hospital environment.     

The content of hippocampal “replay”

One of the most striking features of the hippocampal network is its ability to self‐generate neuronal sequences representing temporally compressed, spatially coherent paths. These brief events, often termed “replay” in the scientific literature, are largely confined to non‐exploratory states such as sleep or quiet rest. Early studies examining the content of replay noted a strong correlation between the encoded spatial information and the animal's prior behavior; thus, replay was initially hypothesized to play a role in memory formation and/or systems‐level consolidation via “off‐line” reactivation of previous experiences. However, recent findings indicate that replay may also serve as a memory retrieval mechanism to guide future behavior or may be an incidental reflection of pre‐existing network assemblies. Here, I will review what is known regarding the content of replay events and their correlation with past and future actions, and I will discuss how this knowledge might inform or constrain models which seek to explain the circuit‐level mechanisms underlying these events and their role in mnemonic processes.