The functional and structural differences between bilateral corresponding brain areas are collectively summarized as hemispheric laterality and could play a key role in behavior and cognition. The habenula is an evolutionarily conserved brain structure in the epithalamus acting as a relay hub between the forebrain and the hindbrain thereby modulating behaviors affected by negative emotions such as stress and anxiety. Anatomical asymmetry of the habenula is well established in fish, but asymmetry in terms of synapse physiology is unknown in any organism. Moreover, there is no macroscopic, anatomical, or functional evidence for medial habenular asymmetry in mammalian. My project aims to reveal such hemispheric differences in function by incorporating acute slice electrophysiology, chemogenetic manipulation, and behavioral experiments. In my talk, I will give some updates about our recent discoveries showing the physiological, and synaptic left-right differences in the medial habenula to the interpeduncular nucleus pathway for the very first time and their potential relevance in emotional memory in mice.