Spatial memory and the human hippocampus

The hippocampus and adjacent medial temporal lobe structures are known to support declarative memory, but there is not consensus about what memory functions the hippocampus might support that are distinct from the functions of the adjacent cortex. One idea is that the hippocampus is specifically important for allocentric spatial memory, e.g., the hippocampus is especially needed to remember object locations when there is a shift in viewpoint between study and test. We tested this proposal in two experiments. Patients with damage limited to the hippocampus were given memory tests for object locations in a virtual environment. In the first experiment, participants studied locations of a variable number of images (one to five) and tried to remember the image locations from either the same viewpoint as during study (shift of 0 degrees) or a different viewpoint (shift of 55 degrees, 85 degrees, or 140 degrees). In each viewpoint condition (shifts of 0 degrees, 55 degrees, 85 degrees, and 140 degrees), patients performed normally when remembering one or two image locations. Further, performance declined to a similar degree in each viewpoint condition as patients tried to remember increasing numbers of image locations. In the second experiment, participants tried to remember four images after viewpoint shifts of 0 degrees, 55 degrees, 85 degrees, or 140 degrees. Patients were mildly impaired at all conditions (shifts of 0 degrees, 55 degrees, 85 degrees, and 140 degrees), and the impairment was no greater when viewpoint shifted. We conclude that damage to the hippocampus does not selectively impair viewpoint-independent spatial memory. Rather, hippocampal damage impairs memory as the memory load increases.     

Anxiety-like behaviors in mice lacking GIT2

G protein-coupled receptor kinase-interactor 2 (GIT2) is a signaling scaffold protein that also functions as GTPase-activating protein (GAPs) for ADP-ribosylation factor (Arf) small GTP-binding proteins. GIT2 has been implicated in the regulation of G protein-coupled receptor trafficking and cell adhesion and migration. To evaluate possible neurobehavioral functions of GIT2 in vivo, we evaluated GIT2-knockout (KO) mice for abnormalities in emotionality and mood. Male and female GIT2-KO mice presented with anxiety-like behaviors in the zero-maze and light–dark emergence tests. Immobility times in tail suspension were reduced in GIT2-KO males, but were normal in GIT2-KO females. Hence, GIT2-KO mice display anxiety-like behavior in an absence of depressive-like responses.     

Impaired fear response in mice lacking GIT1

G protein-coupled receptor kinase interacting protein 1 (GIT1) belongs to the family of Arf GAP proteins and has been implicated in the regulation of G protein-coupled receptor (GPCR) sequestration, cell migration, synapse formation and dendritic spine morphogenesis in neurons. To extend these cellular studies on GIT1 to an in vivo system, we generated mice with globally inactivated Git1 gene by breeding mice carrying a conditional Git1^flox allele with mice expressing the CMV-Cre transgene. Although many GIT1 knockout (GIT1-KO) animals died shortly after birth, homozygous mutants that survived the early post-partum period developed normally into adulthood and were fertile. Behavioral analyses of adult GIT1-KO mice revealed normal exploratory, anxiety- and depressive-like behaviors. However, GIT1-KO mice show impaired responses to fear conditioning and fear-potentiated startle. Overall, these findings suggest that GIT1 is involved in the regulation of amygdala-mediated experience-based emotional behaviors.     

Polyomaviruses KI and WU in children with respiratory tract infection

The polyomaviruses KI (KIPyV) and WU (WUPyV) have recently been discovered in specimens from patients with respiratory tract infections. To analyze the frequency and clinical impact in a cohort of pediatric patients in a German University Children’s Hospital. Nasopharyngeal aspirates or bronchoalveolar lavage specimens of 229 children with acute respiratory tract infection were screened for KIPyV and WUPyV using polymerase chain reaction-based methods. KIPyV was detected in 2 (0.9%) and WUPyV in 1 (0.4%) patients, without co-infections with other respiratory viruses but with co-detection of CMV, EBV and HHV 6 in one immunocompromised patient. Only a very small proportion (1.3%) of positive samples for KIPyV and WUPyV was documented in this study; the clinical relevance of these viruses remains unclear and requires further evaluation.     

Role of the hippocampus in remembering the past and imagining the future

It has been proposed that a core network of brain regions, including the hippocampus, supports both past remembering and future imagining. We investigated the importance of the hippocampus for these functions. Five patients with bilateral hippocampal damage and one patient with large medial temporal lobe lesions were tested for their ability to recount autobiographical episodes from the remote past, the recent past, and to imagine plausible episodes in the near future. The patients with hippocampal damage had intact remote autobiographical memory, modestly impaired recent memory, and an intact ability to imagine the future. The patient with large medial temporal lobe lesions had intact remote memory, markedly impaired recent memory, and also had an intact ability to imagine the future. The findings suggest that the capacity for imagining the future, like the capacity for remembering the remote past, is independent of the hippocampus.     

Inducing impulsivity leads high and low restrained eaters into overeating, whereas current dieters stick to their diet

Previous research has related impulsivity to overeating and obesity. However, the precise nature of this relation has not been examined yet. One possibility is that impulsivity causes overeating and hence contributes to overweight. To test this possibility we induced impulsivity versus inhibition to see whether this would affect food intake. In the first study participants were cognitively primed with the concepts “impulsivity” or “inhibition”. Caloric intake was significantly higher in the Impulsivity Condition compared to the Inhibition Condition. This effect was even stronger for highly restrained participants. In the second study impulsivity was manipulated via behavioural instructions. Restrained and unrestrained nondieters acted as expected: their caloric intake was significantly higher when impulsivity was induced compared to inhibition. Current dieters sharply reduced their caloric intake following the impulsivity induction. These results are in accordance with Lowe's model that, contrary to restraint theory, states that restraint and current dieting are different constructs that affect eating regulation differently. At least for nondieters it can be concluded that heightened impulsivity versus inhibition leads to a higher food intake in the lab.