Olfactory hallucination3/13/2023 The OFC is the expectation of reward/punishment in response to stimuli. The orbitofrontal cortex (OFC) is heavily correlated with the cingulate gyrus and septal area to act out positive/negative reinforcement. The parahippocampal gyrus houses the topographical map for olfaction. Similarly, the parahippocampus encodes, recognizes and contextualizes scenes. The hippocampus forms new and reinforces existing memories. The hippocampus (although minimally connected to the main olfactory bulb) receives almost all of its olfactory information via the amygdala (either directly or via the BNST). Mitral pulses to the hypothalamus promote/discourage feeding, whereas accessory olfactory bulb pulses regulate reproductive and odor-related-reflex processes. BNST also connects to the septal area, rewarding sexual behavior. BNST abnormalities often lead to sexual confusion and immaturity. Stria terminalis, specifically bed nuclei (BNST), act as the information pathway between the amygdala and hypothalamus, as well as the hypothalamus and pituitary gland. The main olfactory bulb's pulses in the amygdala are used to pair odors to names and recognize odor to odor differences. The info for these processes comes from the vomeronasal organ indirectly via the olfactory bulb. Allomones include flower scents, natural herbicides, and natural toxic plant chemicals. Due to cerebrum evolution this processing is secondary and therefore is largely unnoticed in human interactions. The amygdala (in olfaction) processes pheromone, allomone, and kairomone (same-species, cross-species, and cross-species where the emitter is harmed and the sensor is benefited, respectively) signals. An oversimplification of its role is to state that it: checks to ensure odor signals arose from actual odors rather than villi irritation, regulates motor behavior (primarily social and stereotypical) brought on by odors, integrates auditory and olfactory sensory info to complete the aforementioned tasks, and plays a role in transmitting positive signals to reward sensors (and is thus involved in addiction). *In total it has 27 inputs and 20 outputs. The olfactory tubercle connects to numerous areas of the amygdala, thalamus, hypothalamus, hippocampus, brain stem, retina, auditory cortex, and olfactory system. The uncus houses the olfactory cortex which includes the piriform cortex (posterior orbitofrontal cortex), amygdala, olfactory tubercle, and parahippocampal gyrus. How the bulbar neural circuit transforms odor inputs to the bulb to the bulbar responses that are sent to the olfactory cortex can be partly understood by a mathematical model. The cells are different with mitral having low firing-rates and being easily inhibited by neighboring cells, while tufted have high rates of firing and are more difficult to inhibit. These cells also note differences between highly similar odors and use that data to aid in later recognition. The main olfactory bulb transmits pulses to both mitral and tufted cells, which help determine odor concentration based on the time certain neuron clusters fire (called 'timing code'). Mucus also covers the olfactory epithelium, which contains mucous membranes that produce and store mucus, and olfactory glands that secrete metabolic enzymes found in the mucus. Inside the nasal cavity, mucus lining the walls of the cavity dissolves odor molecules. Odor molecules can enter the peripheral pathway and reach the nasal cavity either through the nostrils when inhaling ( olfaction) or through the throat when the tongue pushes air to the back of the nasal cavity while chewing or swallowing (retro-nasal olfaction). The primary components of the layers of epithelial tissue are the mucous membranes, olfactory glands, olfactory neurons, and nerve fibers of the olfactory nerves. The peripheral olfactory system consists mainly of the nostrils, ethmoid bone, nasal cavity, and the olfactory epithelium (layers of thin tissue covered in mucus that line the nasal cavity). This diagram linearly (unless otherwise mentioned) tracks the projections of all known structures that allow for olfaction to their relevant endpoints in the human brain.
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