Takao Inoue

Categorization of biologically significant objects, food and gender, in rhesus monkeys: I. Behavioral study

Macaque monkeys have a highly evolved visual system comparable to that of humans. One of the important visual functions is performing discriminations among biologically significant objects such as food or heterosexual partners. In the present study, we examined whether rhesus monkeys could categorize two-dimensional images related to food or gender using a visual discrimination task. Three rhesus monkeys were trained to make distinctions of food from non-food items, and between male and female monkeys, using 60 or more different pictures of each category. After more than 9 months of training, the monkeys discriminated a variety of foods from non-food and different males from females with more than 80% accuracy, even when the stimuli were used for the first time or presented only once in a session. The proportion of correct responses and response latencies showed better performance in discrimination of food/non-food than that of gender. The results suggest that rhesus monkeys are able to perform visual discrimination of highly abstract biologically significant categories with better performance in a food-related category than a gender-related one, using two-dimensional visual information.

13. Development of a functional mapping method using focal cortical cooling in awake craniotomy

The aim of this study is to determine the usefulness of abnormal muscle response (AMR) and facial motor evoked potential (FMEP) monitoring in predicting outcomes in patients with hemifacial spasm (HFS) who undergo microvascular decompression (MVD). AMRs were recorded from the mentalis and orbicularis oculi muscles. FMEPs were recorded from the orbicularis oculi muscle by transcranial stimulation via corkscrew electrodes placed at positions C3 or C4 and Cz. In 40 95%) of 42 patients, in whom either the amplitude of AMRs decreased <50% or the FMEP amplitude ratios (post/pre MVD) were <100%, the HFS resolved postoperatively. The remaining two patients had recurrences of their spasm 3 months after surgery. In 14 (70%) of 20 of the patients with persistent AMR after MVD, HFS gradually decreased over a mean of 6 weeks and disappeared. On the other hand, in 19 (95%) of the 20 patients with resolved MR, HFS disappeared immediately after MVD. Thus, the AMR findings significantly correlated with postoperative courses (p < 0.001). Our results suggest that both AMR monitoring and FMEP monitoring predict outcomes after MVD in HFS patients. The AMR findings also predict whether the HFS disappears immediately or gradually after surgery.

Category Recognition in the Monkey Orbitofrontal Cortex

The orbitofrontal cortex (OBF) is known to play important roles in evaluation of reward value based on integration of multimodal sensory inputs. In this study, we investigated the complex cognitive functions in the OBF neurons from rhesus monkeys (Macaca mulatta). Glass-coated Elgiloy electrodes and tungsten fiber multi-barreled glass microelectrodes have been used for extracellular recording during behaving the visual discrimination task. As a result, Neurons showed a wide variety of selectivity for these complex images. OBF neurons are involved in various levels of categorization and integrate various endogenous humoral signals and specific exogenous sensory cues.

Hole escape processes detrimental to photoluminescence efficiency in a blue InGaN multiple-quantum-well diode under reverse bias conditions

Photoluminescence (PL) properties of a blue In0.3Ga0.7N multiple-quantum-well (MQW) diode with an additional n+-doped In0.18Ga0.82N electron reservoir layer (ERL) have been investigated at 20K as a function of reverse bias under indirect barrier excitation. A PL intensity ratio of MQW/ERL is observed to be significantly quenched by increasing the reverse field due to electron-hole separation and carrier escape, in spite of observed blueshifts, when the excitation power is decreased by two orders of magnitude. The PL intensity reduction suggests that the hole escape process plays an important role for determination of the PL efficiency under the reverse bias.

External Field Effects on Photoluminescence Properties of Blue InGaN Quantum-Well Diodes

Photoluminescence (PL) properties of blue InGaN quantum-well light-emitting diodes have been investigated at 20 K as a function of excitation power and reverse bias voltage (external field). PL intensity reduction of the main blue emission band is observed by increasing the reverse field. The photoexcitation power dependence suggests that the hole escape process plays an important role for the determination of PL intensity under the reverse bias conditions.