Processing of tactile information by the hippocampus.

The ability to detect unusual events occurring in the environment is essential for survival. Several studies have pointed to the hippocampus as a key brain structure in novelty detection, a claim substantiated by its wide access to sensory information through the entorhinal cortex and also distinct aspects of its intrinsic circuitry. Novelty detection is implemented by an associative match-mismatch algorithm involving the CA1 and CA3 hippocampal subfields that compares the stream of sensory inputs received by CA1 to the stored representation of spatiotemporal sequences in CA3. In some rodents, including the rat, the highly sensitive facial whiskers are responsible for providing accurate tactile information about nearby objects. Surprisingly, however, not much is known about how inputs from the whiskers reach CA1 and how they are processed therein. Using concurrent multielectrode neuronal recordings and chemical inactivation in behaving rats, we show that trigeminal inputs from the whiskers reach the CA1 region through thalamic and cortical relays associated with discriminative touch. Ensembles of hippocampal neurons also carry precise information about stimulus identity when recorded during performance in an aperture-discrimination task using the whiskers. We also found broad similarities between tactile responses of trigeminal stations and the hippocampus during different vigilance states (wake and sleep). Taken together, our results show that tactile information associated with fine whisker discrimination is readily available to the hippocampus for dynamic updating of spatial maps.

Grief, Mindfulness and Neural Predictors of Improvement in Family Dementia Caregivers.

Background: Family dementia caregivers often suffer from an immense toll of grief while caring for their loved ones. We sought to identify the clinical relationship between grief, depression and mindfulness and identify neural predictors of symptomatology and improvement. Methods: Twenty three family dementia caregivers were assessed at baseline for grief, mindfulness and depression, of which 17 underwent functional magnetic resonance imaging (fMRI). During fMRI, caregivers were shown faces of either their dementia-stricken relative or that of a stranger, paired with grief-related or neutral words. In nine subjects, post fMRI scans were also obtained after 4 weeks of either guided imagery or relaxation. Robust regression was used to predict changes in symptoms with longitudinal brain activation (BA) changes as the dependent variable. Results: Grief and depression symptoms were correlated (r = 0.50, p = 0.01), and both were negatively correlated with mindfulness (r = -0.70, p = 0.0002; r = -0.52, p = 0.01). Relative to viewing strangers, caregivers showed pictures of their loved ones (picture factor) exhibited increased activation in the dorsal anterior cingulate gyrus and precuneus. Improvement in grief but not mindfulness or depression was predicted by increased relative BA in the precuneus and anterior cingulate (different subregions from baseline). Viewing grief-related vs. neutral words elicited activity in the medial prefrontal cortex and precuneus. Conclusions: Caregiver grief, depression and mindfulness are interrelated but have at least partially nonoverlapping neural mechanisms. Picture and word stimuli related to caregiver grief evoked brain activity in regions previously identified with bereavement grief. These activation foci might be useful as biomarkers of treatment response.