BOOM I GOT IT :D !!
excitatory postsynaptic input at dendrides = negative outer extracelluar fuid (cause positive ions rush inside the neuron cause its depolarizing)
—> in radial dipoles (form gyri) (so those standing on end so dendrites closest to scalp egg then picks up thsi negative charged extracellualr fluid and will show a negative deflection.
—> positive ions will flow out at other end of neuron ( the SOMA), so positive extracellular fluid there. BUT because dendrite end with more negative extracellular fuid closer to scalp a negative deflection is measured.
—> can also be inhibitory postsynaptic input on soma end cause would negatively charge inside of some so more positive ions in extracellular fluid which means less positive ions in dendride extracellular fluid :D !! WOOP WOOP :D!!!
However, if excitatory postynaptic potential at soma, then that leads to negatively charged extracellular fluid there cause positive charge rushe s into the cell because depolarisation, which leads to positive charge on dendrite end (cause positive ions move out to send on the action potential, which is then measured as a positive deflection)!!
—> could also be inhibitory postsynaptic input at dendrites cause would mean less positive ions in dendrites , so so more outside in extracellular fluid at dendrite end and less positive ions at soma end so negative charged extracellular fluid there :3 !!