Structure and Function of the Olfactory Bulb - The olfactory bulb is located on the inferior side of the brain in humans and is divided into the main olfactory bulb and the accessory olfactory bulb. - The main olfactory bulb connects to the amygdala and plays a role in odor detection and discrimination. - Destruction of the olfactory bulb results in ipsilateral anosmia. - The olfactory bulb has a multi-layered cellular architecture, including the glomerular layer, external plexiform layer, mitral cell layer, internal plexiform layer, and granule cell layer. - The olfactory bulb enhances the sensitivity of odor detection and filters out background odors to enhance the transmission of select odors. - The olfactory bulb permits higher brain areas involved in arousal and attention to modify the detection or discrimination of odors.

Temporal Processing and Lateral Inhibition in the Olfactory Bulb - Processing occurs at each level of the main olfactory bulb, with interneurons in the external plexiform layer exhibiting both excitatory and inhibitory potentials. - Neural firing in the olfactory bulb varies temporally, and synchronised mitral cell spike trains help discriminate similar odors better. - Lateral inhibition, mediated by interneurons in the external plexiform layer, aids in odor discrimination by decreasing firing in response to background odors. - The granule cell layer, which connects mitral cells and interneurons known as granule cells, plays a crucial role in lateral inhibition and differentiated odor responses.

Accessory Olfactory Bulb and Further Processing of Olfactory Information - The accessory olfactory bulb forms a parallel pathway independent from the main olfactory bulb and receives input from the vomeronasal organ, involved in social and reproductive behaviors. - Olfactory information from the olfactory bulb is further processed in the amygdala, orbitofrontal cortex (OFC), and hippocampus. - The amygdala is involved in associative learning between odors and behavioral responses, while the OFC assesses the value and nutritional content of a food reward. - The hippocampus aids in olfactory memory and learning, including the formation of episodic memory.

Olfactory Coding in Habenula and Depression Models - Neurons in the hippocampus and habenula fire in response to odor stimuli, and the dorsal habenula shows functional asymmetry with predominant odor responses in the right hemisphere. - Olfactory bulb removal in rats causes structural changes in the amygdala and hippocampus, leading to behavioral changes similar to depression. - Decreased neuroplasticity in the hippocampus is observed after olfactory bulb removal, which is associated with behavioral changes characteristic of depression.

Adult Neurogenesis and Role of the Hippocampus and Amygdala - The olfactory bulb, subventricular zone, and subgranular zone of the hippocampus undergo continuing neurogenesis in adult mammals. - New neurons in the olfactory bulb may participate in learning processes and are sensitive to olfactory activity. - The hippocampus and amygdala influence odor perception and associate odors with emotions and rewards. - The orbitofrontal cortex contributes to appetite regulation and projects to the anterior cingulate cortex.