Complete and dorsal hippocampal lesions impaired spatial performance on 2 working memory tasks: rewarded alternation on the T maze and matching to position in the water maze. In contrast, ventral hippocampal lesions had no effect on these tasks, even when task difficulty was increased by the introduction of delays. Ventral lesions did resemble complete lesions in reducing anxiety in 3 commonly used tests of anxiety (social interaction, plus-maze, and hyponeophagia). Dorsal lesions also appeared to be anxiolytic in the social interaction and plus-maze tests, but they did not affect hyponeophagia. Complete- and dorsal-lesioned rats displayed hyperactivity, whereas ventral-lesioned rats did not. These results show a double dissociation between dorsal and ventral hippocampal lesions (hyponeophagia vs. spatial memory), suggesting differentiation of function along the septotemporal axis of this structure.

We measured cortical activity with functional magnetic resonance imaging to probe the involvement of early visual cortex in visual short-term memory and visual attention. In four experimental tasks, human subjects viewed two visual stimuli separated by a variable delay period. The tasks placed differential demands on short-term memory and attention, but the stimuli were visually identical until after the delay period. Early visual cortex exhibited sustained responses throughout the delay when subjects performed attention-demanding tasks, but delay-period activity was not distinguishable from zero when subjects performed a task that required short-term memory. This dissociation reveals different computational mechanisms underlying the two processes.

Objective To test that cerebral atrophy is associated with increased risk for development of chronic subdural haematoma (cSDH), this study performed volumetric analysis of computed tomography (CT) brain scans from patients who were diagnosed with cSDH on subsequent CT scans and their age-matched controls. Methods Volumetric analysis was performed on CT scans acquired a mean of 209 days prior to cSDH diagnosis in 19 patients. Cerebral atrophy present on these scans was then compared to 76 age-matched control patients randomly selected from cSDH-free subjects. Results There was a higher degree of atrophy in cSDH patients (n =19, 14.3% ± 5.4%) than in age-matched control patients (n =76, 11.9% ± 5.5%; p =0.044). Logistical regression demonstrated that atrophy was found to be a significant predictor of cSDH at all ages (OR =1.11, 95% CI =[1.01, 1.23], p =0.05). For younger subjects ≤65 years of age (n =50), atrophy was an even stronger predictor of cSDH (OR =1.17, 95% CI =[1.02, 1.34], p =0.026). Conclusions Cerebral atrophy is associated with the development of cSDH and this association is greater in patients ≤65 years of age.

Brouwer GJ, Arnedo V, Offen S, Heeger DJ, Grant AC. Normalization in human somatosensory cortex. J Neurophysiol 114: 2588 -2599, 2015. First published August 26, 2015 doi:10.1152/jn.00939.2014.-Functional magnetic resonance imaging (fMRI) was used to measure activity in human somatosensory cortex and to test for cross-digit suppression. Subjects received stimulation (vibration of varying amplitudes) to the right thumb (target) with or without concurrent stimulation of the right middle finger (mask). Subjects were less sensitive to target stimulation (psychophysical detection thresholds were higher) when target and mask digits were stimulated concurrently compared with when the target was stimulated in isolation. fMRI voxels in a region of the left postcentral gyrus each responded when either digit was stimulated. A regression model (called a forward model) was used to separate the fMRI measurements from these voxels into two hypothetical channels, each of which responded selectively to only one of the two digits. For the channel tuned to the target digit, responses in the left postcentral gyrus increased with target stimulus amplitude but were suppressed by concurrent stimulation to the mask digit, evident as a shift in the gain of the response functions. For the channel tuned to the mask digit, a constant baseline response was evoked for all target amplitudes when the mask was absent and responses decreased with increasing target amplitude when the mask was concurrently presented. A computational model based on divisive normalization provided a good fit to the measurements for both mask-absent and target ϩ mask stimulation. We conclude that the normalization model can explain cross-digit suppression in human somatosensory cortex, supporting the hypothesis that normalization is a canonical neural computation.

Cortical activity was measured with functional magnetic resonance imaging to probe the involvement of the superior precentral sulcus (including putative human frontal eye fields, FEF) and the intraparietal sulcus (IPS) in visual short term memory and visual attention. In two experimental tasks, human subjects viewed two visual stimuli separated by a variable delay period. The tasks placed differential demands on short-term memory and attention, but the stimuli were visually identical until after the delay period. An earlier study (Offen, Schluppeck, & Heeger, 2009) had found a dissociation in early visual cortex that suggested different computational mechanisms underlying the two processes. In contrast, the results reported here show that the patterns of activation in prefrontal and parietal cortex were different from one another but were similar for the two tasks. In particular, the FEF showed evidence for sustained delay-period activity for both the working memory and the attention task, while the IPS did not show evidence for sustained delay-period activity for either task. The results imply differential roles for the FEF and IPS in these tasks; the results also suggest that feedback of sustained activity from frontal cortex to visual cortex might be gated by task demands.