Putting objects in context: A prefrontal-hippocampal-perirhinal cortex network.

When we encounter an object, we spontaneously form associations between the object and the environment in which it was encountered. These associations can take a number of different forms, which include location and context. A neural circuit between the hippocampus, medial prefrontal cortex and perirhinal cortex is critical for object-location and object-sequence associations; however, how this neural circuit contributes to the formation of object-context associations has not been established. Bilateral lesions were made in the hippocampus, medial prefrontal cortex or perirhinal cortex to examine each region contribution to object-context memory formation. Next, a disconnection lesion approach was used to examine the necessity of functional interactions between the hippocampus and medial prefrontal cortex or perirhinal cortex. Spontaneous tests of preferential exploration were used to assess memory for different types of object-context associations. Bilateral lesion in the hippocampus, medial prefrontal cortex or perirhinal cortex impaired performance in both an object-place-context and an object-context task. Disconnection of the hippocampus from either the medial prefrontal cortex or perirhinal cortex impaired performance in both the object-place-context and object-context task. Interestingly, when object recognition memory was tested with a context switch between encoding and test, performance in the hippocampal and medial prefrontal cortex lesion groups was disrupted and performance in each disconnection group (i.e. hippocampus + medial prefrontal cortex, hippocampus + perirhinal cortex) was significantly impaired. Overall, these experiments establish the importance of the hippocampal-medial prefrontal-perirhinal cortex circuit for the formation of object-context associations.

Remembering the order of serially presented objects: A matter of time?

Remembering the sequence, in which stimuli are encountered or events have occurred, is a key process in episodic memory and can also facilitate recognition memory. Rodents, when presented with a sequence of objects, will explore the object encountered first; yet, whether this behaviour is because the rodents spontaneously encode the order of stimuli presentation or because of relative familiarity or temporal decay is unknown. Here, we tested sequence memory in rats using a series of spontaneous preference tasks. Experiment 1 demonstrated that when rats are presented with a sequence of four objects, with an inter-sample interval of 5 min or 1 h, they preferentially explored the object presented earlier in the list irrespective of the inter-sample interval. We then demonstrated that such memory for order was not affected by increasing or decreasing the inter-sample interval between the middle objects (Experiment 2). Finally, we showed that memory for order is not a function of absolute object familiarity, as animals showed clear discrimination between the objects presented in the sample phases and a novel object, independent of the sample objects' position in the sequence (Experiment 3). These results show that animals are able to encode the order of objects presented in a sequence, and as such temporal order memory is not achieved using the process of relative or absolute familiarity or temporal decay.

What pharmacological interventions indicate concerning the role of the perirhinal cortex in recognition memory.

Findings of pharmacological studies that have investigated the involvement of specific regions of the brain in recognition memory are reviewed. The particular emphasis of the review concerns what such studies indicate concerning the role of the perirhinal cortex in recognition memory. Most of the studies involve rats and most have investigated recognition memory for objects. Pharmacological studies provide a large body of evidence supporting the essential role of the perirhinal cortex in the acquisition, consolidation and retrieval of object recognition memory. Such studies provide increasingly detailed evidence concerning both the neurotransmitter systems and the underlying intracellular mechanisms involved in recognition memory processes. They have provided evidence in support of synaptic weakening as a major synaptic plastic process within perirhinal cortex underlying object recognition memory. They have also supplied confirmatory evidence that that there is more than one synaptic plastic process involved. The demonstrated necessity to long-term recognition memory of intracellular signalling mechanisms related to synaptic modification within perirhinal cortex establishes a central role for the region in the information storage underlying such memory. Perirhinal cortex is thereby established as an information storage site rather than solely a processing station. Pharmacological studies have also supplied new evidence concerning the detailed roles of other regions, including the hippocampus and the medial prefrontal cortex in different types of recognition memory tasks that include a spatial or temporal component. In so doing, they have also further defined the contribution of perirhinal cortex to such tasks. To date it appears that the contribution of perirhinal cortex to associative and temporal order memory reflects that in simple object recognition memory, namely that perirhinal cortex provides information concerning objects and their prior occurrence (novelty/familiarity).

Evaluating the neural basis of temporal order memory for visual stimuli in the rat.

Temporal order memory (memory for stimulus order) is crucial for discrimination between familiar objects and depends upon a neural circuit involving the perirhinal cortex (PRH) and medial pre-frontal cortex. This study examined the role of glutamatergic and cholinergic neurotransmission in the encoding or retrieval of temporal order memory, using a task requiring the animals to discriminate between two familiar objects presented at different intervals. 6-Cyano-7-nitroquinoxaline (CNQX) (AMPA/kainate receptor antagonist), scopolamine (muscarinic receptor antagonist) or 2-amino-5-phosphonopentanoic acid (AP5) (N-methyl-D-aspartate receptor antagonist) was administered before sample phase 2 (to be active during encoding) or before test (to be active during retrieval). Unilateral CNQX administration into the PRH and pre-limbic/infra-limbic cortices (PL/IL) in opposite hemispheres, i.e. to disrupt neurotransmission within the circuit, impaired encoding and retrieval. Administration of scopolamine or AP5 in the PRH-PL/IL circuit impaired encoding. Drug effects in each brain region were then investigated separately. Intra-PRH CNQX, scopolamine or AP5 disrupted encoding, such that the animals explored the recent object significantly more than the old object. In contrast, intra-PL/IL CNQX, scopolamine or AP5 impaired memory performance such that the animals spent an equal amount of time exploring the objects. CNQX but not AP5 or scopolamine impaired retrieval. Furthermore, CNQX impaired novel object preference when infused into the PRH but not PL/IL following a 3 h delay. Thus, encoding of temporal order memory is mediated by plastic processes involving N-methyl-D-aspartate and muscarinic receptors within the PRH-PL/IL circuit, but these two regions make qualitatively different cognitive contributions to the formation of this memory process.

A role for calcium-calmodulin-dependent protein kinase II in the consolidation of visual object recognition memory.

The aim was to investigate the role of calcium-calmodulin-dependent protein kinase (CAMK)II in object recognition memory. The performance of rats in a preferential object recognition test was examined after local infusion of the CAMKII inhibitors KN-62 or autocamtide-2-related inhibitory peptide (AIP) into the perirhinal cortex. KN-62 or AIP infused after acquisition impaired memory tested at 24 h, indicating an involvement of CAMKII in the consolidation of recognition memory. Memory was impaired when KN-62 was infused at 20 min after acquisition or when AIP was infused at 20, 40, 60 or 100 min after acquisition. The time-course of CAMKII activation in rats was further examined by immunohistochemical staining for phospho-CAMKII(Thre286)alpha at 10, 40, 70 and 100 min following the viewing of novel and familiar images. At 70 min, processing novel images resulted in more phospho-CAMKII(Thre286)alpha-stained neurons in the perirhinal cortex than did the processing of familiar images, consistent with the viewing of novel images increasing the activity of CAMKII at this time. This difference was eliminated by prior infusion of AIP. These findings establish that CAMKII is active within the perirhinal region between approximately 20 and 100 min following learning and then returns to baseline. Thus, increased CAMKII activity is essential for the consolidation of long-term object recognition memory but continuation of that increased activity throughout the 24 h memory delay is not necessary for maintenance of the memory.

Serum IgG antibodies to Helicobacter pylori in patients with recurrent aphthous stomatitis and other oral disorders.

OBJECTIVES: To compare the frequency of serum anti-Helicobacter pylori IgG antibodies in patients with recurrent aphthous stomatitis with patients with other oral ulcerative and nonulcerative disorders. STUDY DESIGN: Prospective study of serum IgG antibodies to H. pylori in 75 patients with recurrent aphthous ulcers, 15 patients with other oral ulcerative disorders, 41 patients with other oral mucosal lesions, 27 patients with oral dysaesthesia, and 25 healthy control patients without oral lesions. RESULTS: The frequency of anti-H, pylori seropositivity was not significantly greater in patients with recurrent aphthous stomatitis (30.6%) compared with patients with other ulcerated oral mucosal lesions (33.0%) and controls (24%). CONCLUSIONS: Helicobacter pylori does not appear to be of etiologic significance in the development of recurrent aphthous stomatitis.

Experience with the Astra dental implant system.

The Astra Dental Implant System appears to be a relatively successful and economical method of osseointegration. This article lists its clinical components, explains how the system is fitted and discusses the preliminary results.

The facial nerve function coefficient: analysis of 100 normal subjects.

The Facial Nerve Function Index (FNFI) is a measure of asymmetrical facial movement and is a quick and easy method of monitoring the improvement of function in patients with facial nerve palsy. However, purely as a consequence of the way the index is formulated, and not primarily because of any tendency to biological asymmetry favoring one particular direction in the population, the FNFI has a highly skewed distribution. To remove the inherent asymmetry of the index, a modified index, the Facial Nerve Function Coefficient (FNFC), for which a symmetrical distribution is obtained, is proposed. A reference range for this index was derived.

Prosthetic rehabilitation of the edentulous patient requiring a partial maxillectomy.

A variety of problems faces the prosthodontist attempting reconstruction of maxillary defects. This article reviews developments in materials and techniques of obturator prosthesis design for patients experiencing maxillectomy. The size of the maxillectomy defect is one of the main factors governing the prognosis for treatment. Many patients require special prosthodontic techniques. However, routine attention to extension of the prosthesis and balanced occlusion is essential. Obtaining satisfactory retention and stability in the definitive obturator prosthesis can be elusive. Resilient denture base materials are extremely useful in retaining the prosthesis, which obturates small defects. However, the flexibility of these materials makes them unsuitable in large maxillectomy cavities because of the deformation that occurs during mastication. Alternative forms of retention, eg., osseointegrated implants and sectional prostheses retained by magnets, are discussed.

Predominant cultivable flora in pericoronitis.

The predominant cultivable flora in pericoronitis was investigated by culturing pus from affected sites in 20 patients. Twenty colonies were picked at random from non-selective plates and identified using conventional biochemical and physiological tests, analysis of metabolic end-products by gas chromatography and protein profile analysis. The most frequently isolated organisms were Prevotella (Bacteroides) intermedia, Peptostreptococcus micros, Veillonella species, Fusobacterium nucleatum and Streptococcus mitis. Porphyromonas (Bacteroides) gingivalis was not isolated and asaccharolytic Eubacterium species were virtually absent. The predominant cultivable microflora in pericoronitis was found to be highly anaerobic in nature and superficially similar to that found in chronic periodontitis, although proposed marker organisms of severe periodontitis were absent.

Idiopathic blepharospasm-oromandibular dystonia syndrome (Meige's syndrome) presenting as chronic temporomandibular joint dislocation.

A case of idiopathic blepharospasm-oromandibular dystonia (Meige's syndrome) is reported, presenting as chronic bilateral dislocation of the temporomandibular joints. The nature of the syndrome is discussed, together with the difficulties in diagnosis and management.

A computerized measurement of dental relapse following orthognathic surgery.

A computer-programmed osteotomy package was used to measure agreed values from lateral cephalograms preoperatively, postoperatively, and during the follow-up period. The variable representing the postoperative cephalometric analysis predicted by the program was included for further comparisons. The results were used to measure the degree of dental and skeletal relapse during the follow-up period, but only the dental relapse is discussed in the present study. There was a statistically significant proclination of the maxillary anterior teeth postoperatively that continued during the mean follow-up period of 16 months.

A laboratory assessment of the antimicrobial effectiveness of glove washing and re-use in dental practice.

This study has assessed the ability of five hand-washing agents, Hibisol, Hibiscrub, Betadine, 70% isopropyl alcohol and bar soap, to decontaminate the surfaces of Biogel D, Surgikos Microtouch and Ansell Gammex latex medical gloves after repeated inoculation with Staphylococcus aureus. The glove and hand-washing agents were compared in a Latin Square experiment, and a standardized handwashing regime followed. Each of the gloves used in the study was later tested electrically for micropuncture formation. On the basis of microbial recovery, no specific combination of glove and hand washing agent proved superior, the marker organism being isolated on a sporadic basis. In addition, 17% of the gloves showed evidence of micropunctures after five sequential inoculations and washings. These results suggest that, even under strictly controlled conditions, glove surfaces cannot be reliably and consistently cleaned of microbial contamination, nor can they be guaranteed to remain puncture-free. Ideally, therefore, a new pair of gloves should be worn for each patient.

Cephradine penetration of mandibular bone.

The concentration of cephradine in serum and mandibular bone was assayed in 22 patients undergoing third molar surgery following a single 1-g intramuscular injection. Serum and cortical bone samples taken simultaneously contained mean cephradine concentrations of 12.41 micrograms/mL and 1.25 micrograms/g, respectively. These results, when compared with those reported for other bony sites, including femoral head and knee, show a reduced bone penetration with a bone-to-serum ratio of approximately 0.10:1.

Spectral analysis of the masseter and anterior temporalis: an assessment of reliability for use in the clinical situation.

The electromyogram (EMG) of contracting muscles can be analysed in the frequency domain by spectral analysis. However, there is a need to establish the reproducibility of spectral parameters such as mean power frequency (MPF). This study examined the variation of MPF (masseter and anterior temporalis) between and within recording sessions. The MPF was found to be significantly reliable for both muscles, but considerable within-subject variation was found despite comprehensive measures to standardize recording methods and conditions. It is concluded that MPF may have clinical application in the diagnosis and treatment of patients with facial pain arising from muscle dysfunctions, but caution should be exercised in interpreting small changes in frequency, given the inherent variability of MPF.

Postoperative morbidity with mandibular third molar surgery: a comparison of two techniques.

The postoperative pain and swelling that followed the removal of symmetrically impacted mandibular third molars by the split bone and bur techniques was studied in 30 patients. Removal by the split bone technique produced noticeably less pain and swelling. Interdependence was noted between pain and swelling.